WASHINGTON – New revelations that China used cyberattacks to access data from nearly 40 Pentagon weapons programs and almost 30 other defense technologies have increased pressure on U.S. leaders to take more strident action against Beijing to stem the persistent breaches.

The disclosure, which was included in a Defense Science Board report released earlier this year, but is only now being discussed publicly, comes as Defense Secretary Chuck Hagel heads to Southeast Asia, where he will discuss the escalating cyberthreat with counterparts from a number of area nations.

While officials have been warning for years about China’s cyber espionage efforts aimed at U.S. military and high-tech programs, the breadth of the list underscored how routine the attacks have become. And, as the U.S. looks to grow its military presence in the Asia Pacific, it heightens worries that China can use the information to blunt America’s military superiority and keep pace with emerging technologies.

“It introduces uncertainty on how well the weapons may work, and it means we may have to redo weapons systems,” said James Lewis, a cybersecurity expert at the Center for Strategic and International Studies. “If they know how it works precisely, they will be able to evade it and figure out how to better beat our systems.”

A chart included in the science board’s report laid out what it called a partial list of 37 breached programs, which included the Terminal High Altitude Area Defense weapon — a land-based missile defense system that was recently deployed to Guam to help counter the North Korean threat. Other programs include the F-35 Joint Strike Fighter, the F-22 Raptor fighter jet, and the hybrid MV-22 Osprey, which can take off and land like a helicopter and fly like an airplane.

The report also listed another 29 broader defense technologies that have been compromised, including drone video systems and high-tech avionics. The information was gathered more than two years ago, so some of the data is dated and a few of the breaches — such as the F-35 — had actually already become public.

U.S. officials have been far more open about discussing the China cyberattacks over the past year or two, beginning with a November 2011 report by U.S. intelligence agencies that accused China of systematically stealing American high-tech data for its own national economic gain. The Pentagon, meanwhile, in its latest report on China’s military power, asserted publicly for the first time that Beijing’s military was likely behind computer-based attacks targeting federal agencies.

“In 2012, numerous computer systems around the world, including those owned by the U.S. government, continued to be targeted for intrusions, some of which appear to be attributable directly to the Chinese government and military,” said the report, which was released earlier this month.

The benefits to the cyber espionage are high and the costs are low, said Shawn Henry, former cyber director at the FBI and now president of CrowdStrike Services, a security technology company.

“There is no cost, there are no sanctions, no diplomatic actions, no financial disincentives,” said Henry, adding that the U.S. intellectual property losses are in the hundreds of millions of dollars. He said that the U.S. needs to have a discussion with Chinese leaders about “what the red lines are and what the repercussions will be for crossing those red lines.”