WASHINGTON — For years the deliberate “strategic ambiguity” in Washington’s China policy has left unclear how the United States would respond to a full-scale, amphibious invasion of Taiwan.

But an equally hard question — maybe harder, in the minds of many senior White House and defense officials — is how to respond to a slow squeeze of the island, in which Chinese forces cut off much of the access to it, physically or digitally.

That question may soon be tested for the first time in a quarter of a century. China’s declaration during Speaker Nancy Pelosi’s visit that it would begin live-fire military exercises in six locations encircling the island could set up the largest crisis in the Taiwan Strait since 1996, when President Bill Clinton ordered American aircraft carriers to the area.

But those exercises were significantly farther from Taiwan’s shores than the series the Chinese government has warned mariners and aircraft that it plans. And it took place in a far more benign strategic environment, back when China’s entry into the global economy was supposed to modify its behavior, and when Mr. Clinton would tell Chinese students that the spread of the internet would foster freedom and dissent. It was also when China’s military packed a fraction of the punch it now boasts, including anti-ship missiles developed to deter American warships from getting close.

Administration officials say that based on their assessments a full cutoff of access to Taiwan is unlikely — in large part because it would hurt China’s own economy at a time of severe economic slowdown. On Friday, the Group of 7 industrialized nations, the core of the Western alliance, warned China not to retaliate for Ms. Pelosi’s visit, clearly an effort to suggest that China would be widely condemned for overreacting, much as Russia was for its invasion of Ukraine.

But American officials say they worry that the events of the next few days could trigger an unintended confrontation between China’s forces and Taiwan’s, especially if the Chinese military launches a missile over the island, or if an incursion into disputed airspace leads to a midair conflict. Something similar happened 20 years ago, when a Chinese military aircraft collided with an American intelligence-gathering plane.

As the military exercises began early Wednesday, White House and Pentagon officials were monitoring the situation closely, trying to figure out if China was sending forces into each of the areas near Taiwan’s coast it has declared closed. But their assessment was that China’s strategy is to intimidate and coerce, without triggering a direct conflict.

Outside experts were more concerned that the exercise could escalate.

“This is one of the scenarios that is difficult to deal with,’’ said Bonny Lin, who directed the Taiwan desk at the Pentagon and held other defense positions before moving to the Center for Strategic and International Studies in Washington, where she heads the China Power Project. “If a military exercise transitions to a blockade, when does it become clear that the exercise is now a blockade? Who should be the first to respond? Taiwan’s forces? The United States? It’s not clear.”

An exercise-turned-blockade is one of many scenarios that get “war-gamed” in Washington regularly, as American officials try to map out options before a crisis strikes. But nothing really replicates a real-life confrontation.

Mr. Biden, aides say, would have to try to walk the delicate line between avoiding folding to the Chinese and avoiding escalation.

It is even more complicated by the continuing debate over how to help Taiwan become a “porcupine,’’ or a country too well defended for China to invade. For all the talk of F-16 sales to Taiwan — its fleet is supposed to top 200 of the fighter aircraft by 2026 — there is growing worry that Taiwan is buying the wrong kind of gear to defend itself, and that it needs to learn some lessons from Ukraine.

It is hardly a new debate. Two years ago, a senior defense official, David F. Helvey, warned that as China’s ability to choke off the island rises, Taiwan itself can, “through smart investment, send a clear signal to Beijing that Taiwan’s society and its armed forces are committed to the defense of Taiwan.” But he warned that the sums that Taiwan’s government was committing to acquiring new defensive technology were insufficient for a resilient defense.

The result has been a steady drumbeat from Washington urging Taiwan’s leadership to invest less in expensive F-16 fighters and more on what Mr. Helvey called “large numbers of small things,’’ the formula that later helped Ukraine resist Russian forces.

That list includes mobile cruise missiles for coastal defense, naval mines, small fast-attack craft and mobile artillery.

President Tsai Ing-wen of Taiwan has expressed support for the so-called “asymmetric” strategy and has moved in recent years to increase the defense budget and buy many of the small, mobile weapons that U.S. officials have recommended, like Harpoon missiles. But she has encountered resistance at times from some Taiwanese military officials, who argue that some conventional weapons systems are still necessary to prepare for different scenarios. They have also argued that without an explicit security guarantee from the United States, it would be too risky for Taiwan to give up its lethal weapons.

That view has changed somewhat in recent months as the war in Ukraine has jolted Taiwan’s military and the public, prompting a greater embrace of the “porcupine” strategy. But that war has also depleted stocks and strained production capacity among American and allied defense contractors, meaning Taiwan may need to wait for several years. And that delay gives China an opening.

Moreover, Taiwan’s defense budget hovers at around $17 billion a year, though it has committed to spend an additional $8 billion on armaments over the next several years. By comparison, Congress recently apportioned $52 billion in aid for Ukraine — which doesn’t have Taiwan’s revenue streams to pay for its own defense — and China spends on the order of $230 billion annually.

Some also say that what Taiwan needs from the United States is not just weapon sales, but other forms of support, ranging from military technology to operational exchanges and training.

While Taiwan’s military is sometimes allowed to participate in defense symposiums, it is rarely invited to join large multinational military exercises because most countries do not officially recognize it as a nation. And while Washington has gradually ramped up training of Taiwanese forces on the island and in the United States in recent years, the island’s mandatory military service and its reservist program are still seen as insufficiently rigorous.

“The U.S. could help us learn how to train more efficiently and mobilize reserve forces more quickly,” said Ou Si-fu, a research fellow at the Institute for National Defense and Security Research, a think tank affiliated with Taiwan’s defense ministry. “They could also help more in terms of technology transfer, to support our indigenous weapons development programs.”

Of course, defending against invasion bears little resemblance to defending against a blockade. Executing a blockade is even harder.

“Threatening a blockade and actually initiating a blockade are two very different things,” said Eric Sayers, a former senior adviser to the U.S. Pacific Command who is a fellow at the American Enterprise Institute.

Mr. Sayers said China has long had the ability to effectively encircle Taiwan if it chose to do so, so the capability itself isn’t a surprise.

“Despite all the threats Beijing has made in recent weeks, it would still be very difficult for the P.L.A. Navy and costly to China’s economy to maintain a blockade for an extended period of time,” Mr. Sayers added, referring to the People’s Liberation Army. “What hurts Taipei’s economy has a similar effect on Beijing.”

Mr. Sayers continued, “What is most significant about China’s response is that it is giving us a preview of how the P.L.A. might deploy an indirect blockade against Taiwan in the future to ratchet up the pressure near an election or other political crisis.”

“Instead of announcing a military blockade they may instead announce an extended military exercise around Taiwan that closes or disrupts shipping routes for 30, 60, 90 days. This makes it less a military operation and more a form of legal warfare to justify an indirect blockade for a duration that Beijing can manipulate.”

Others say the United States could do more to bolster Taiwan’s security by helping it better integrate into the global economic system. Taiwanese officials and analysts argue that strengthening trade links and possibly passing a bilateral trade agreement could help the island reduce its reliance on China, currently its largest trade partner. But China would undoubtedly consider that an aggressive act.

The geopolitical risks of Taiwan’s dependence on the Chinese market were on display this week when just hours after Ms. Pelosi arrived in Taiwan, Beijing moved to suspend exports of natural sand to the island — key for construction — and banned imports from Taiwan of certain types of fruit and fish.

“Economic security is so important to Taiwan’s survival as a democracy,” said Vincent Chao, former political director at the Taipei Economic and Cultural Representative Office in Washington.

Diversifying American support for Taiwan from arms sales is crucial not only to better defend against China, but also to boost morale for a fellow democratic partner, said Mark Stokes, executive director of the Project 2049 Institute, a defense research group in Arlington, Virginia.

“We shouldn’t just be cramming weapons down their throat and robbing them of their agency in terms of determining what their own defense requirements are,” Mr. Stokes said. “What Taiwan needs most from the U.S. is to be treated, as much as possible given the constraints, as a normal partner with respect.”

Eric Schmitt contributed reporting from Washington.