China is building up its nuclear and missile forces and is mobilizing vast resources to rival the Pentagon’s, the Defense Department said in its annual report on Chinese military power, which concluded that the country’s armed forces in certain areas had eclipsed the U.S. military.

The report, released Tuesday by the Pentagon, comes as the U.S. military shifts its focus from Middle East counterinsurgencies that have dominated its operations for two decades toward a possible future conflict with China and Russia, in what defense leaders have dubbed “an era of great power competition.”

China’s armed forces, the Pentagon said, not only are acquiring sophisticated new technology and weaponry but also are overhauling their organizational structures, as China aims to complete a military modernization by 2035 and establish a “world-class military” that can rival or exceed that of the United States by 2049.

Beijing’s goal, the report says, is then to leverage its new ­military might to achieve its foreign-policy objectives in the Western Pacific and to assert itself globally.

Chad Sbragia, the deputy assistant secretary of defense for China, said at a briefing this week that the Chinese Communist Party views U.S. alliances and partnerships as “destabilizing and irreconcilable with China’s interests.” He described Beijing’s military buildup as a key element of China’s broader effort to “revise the international order.”

“The CCP has not defined exactly what it means by its ambition to have a world-class military,” Sbragia said. “Within the context of China’s national strategy, however, it is likely that China will aim to develop a military by mid-century that is equal to, and in many cases superior to, the United States’ military or that of any other great power that the Chinese view as a threat.”

The Chinese Embassy in Washington did not respond to a request for comment about the report.

The report comes also as Defense Secretary Mark T. Esper completes a visit to Hawaii, Palau and Guam meant to underscore U.S. resolve in the Pacific, and days after China’s military fired ballistic missiles across the disputed South China Sea as part of an annual exercise that the Defense Department described as counterproductive and destabilizing.

Sbragia said the missile launches were part of a string of activities designed by China to intimidate its neighbors.

In its report, the Defense Department concluded that the Chinese military was already ahead of the Pentagon in three critical areas: shipbuilding, air defenses and land-based missiles.

China now has the largest navy in the world, with an overall force of about 350 ships and submarines, compared with the U.S. military’s approximately 293 ships, the report said. Beijing also has one of the world’s most advanced air defense systems, comprising Russian-built S-400 and S-300 surface-to-air missile systems as well as its own domestically produced air defenses.

China has developed a robust missile force, unconstrained by any international arms control agreements, which has made it far more difficult for the United States to defend its allies in the Asia Pacific in the event of a conflict and in particular has shifted the balance of power with neighboring Taiwan.

China has more than 1,250 ground-launch ballistic and cruise missiles in its arsenal with ranges between 500 and 5,500 kilometers (311 and 3,418 miles), the report says. The United States, meanwhile, fields only one ground-launched ballistic missile, with a shorter range, and no ground-launched cruise missiles, according to the report.

Until withdrawing last year, the United States was party to the Intermediate-Range Nuclear Forces Treaty with Russia, which banned the production and deployment of missiles with ranges of 500 to 5,500 kilometers. Since leaving the treaty, the U.S. military has pursued the development of a ground-launch cruise missile, citing in particular the Chinese threat.

In addition to developing hypersonic glide vehicles, which move more than five times the speed of sound, the Chinese have fielded missiles that appear to be particularly aimed at constraining U.S. forces in Asia.

The Pentagon report warns that the Chinese military is advancing its nuclear forces by developing new intercontinental ballistic missiles and by pursuing a full triad that can launch nuclear warheads from air, land and sea.

“Over the next decade, China’s nuclear warhead stockpile — currently estimated to be in the low 200s — is projected to at least double in size as China expands and modernizes its nuclear forces,” the report said, publicly estimating the number of China’s operational nuclear warheads for the first time.

The report also said unspecified developments in 2019 “suggest that China intends to increase the peacetime readiness of its nuclear forces by moving to a launch-on-warning (LOW) posture with an expanded silo-based force.”

A country that adopts a “launch on warning” posture, which the United States maintains with its intercontinental ballistic missile silos, reserves the right to launch nuclear weapons immediately upon detecting an incoming attack.

China previously has said it will retaliate with nuclear weapons only after being struck, in what is known as a “no first use” policy. Beijing has said it is keeping a limited nuclear arsenal for the purposes of “minimum deterrence.”

The report suggests that is changing.

Sbragia said China was moving away from its “historical minimum deterrence posture” and entering a position where it could readily increase the size of its nuclear force.

“We do believe that over the next decade, that China is likely to at least double the size of its nuclear stockpile in the course of implementing the most rapid expansion and diversification of its nuclear arsenal in its history, China’s history,” Sbragia said.

Sbragia called on China to halt its nuclear buildup and join arms-control treaties that have long limited the American and Russian arsenals. China has rejected U.S. entreaties to enter trilateral arms control negotiations with Russia, saying its arsenal is still far smaller than that of Washington’s and Moscow’s. The United States has said that as a global power, China must agree to constraints on its nuclear weapons.

“Combined with a near-complete lack of transparency regarding their strategic intent and the perceived need for a much larger, more diverse nuclear force, these developments pose a significant concern for the United States,” Sbragia said.

The report also emphasized the Chinese military’s global ambitions, as evidenced by the People’s Liberation Army presence at a base in Djibouti in East Africa. Sbragia said the Chinese are looking to open outposts elsewhere in the world, and “there is no area that I know of that’s off the table in terms of where they’re looking at.”

“I think ultimately you will see them pursue locations in every area that you can think of,” Sbragia said.

The Defense Department, which in recent years has focused on waging counterinsurgency operations in Iraq, Afghanistan and Syria, has begun shifting its attention to the threat posed by China — a reorientation that represents a boon for the defense industrial complex because it requires investment in expensive, high-end aircraft, ships and weaponry. Sbragia said China must see the United States responding to its military rise.

“I think that it’s important that they reach that conclusion, that the United States is serious, that it’s undertaking a long-term and strategic transformation of the department for competition,” Sbragia said. “I believe that the Chinese recognize that very clearly.”