(Adds comment from State Department spokeswoman)
By David Brunnstrom and Lesley Wroughton
WASHINGTON, Sept 30 (Reuters) - China is facing growing U.S. pressure to show restraint during mass pro-democracy protests in Hong Kong, with the issue to be raised in high-level U.S.-Chinese talks and a prominent U.S. lawmaker expressing "grave concerns."
A day after the United States backed calls by thousands of protesters for greater autonomy in selecting candidates for Hong Kong's chief executive, U.S. officials said Secretary of State John Kerry would discuss the issue with Chinese Foreign Minister Wang Yi when the two meet in Washington on Wednesday.
"I expect it will come up," State Department spokeswoman Jen Psaki told reporters, referring to the Hong Kong protests. "It is in the news. It is an issue we are concerned about and focused on."
The protesters, mostly students, are demanding full democracy and have called on chief executive Leung Chun-ying to step down after Beijing ruled a month ago that it would vet candidates wishing to run for Hong Kong's leadership in 2017. They have threatened to escalate action over the next few days.
Psaki said Kerry was expected to say that the Hong Kong chief executive's legitimacy would be enhanced if people have a genuine choice of candidates, a position expressed by the White House on Monday that went beyond the administration's previous broad calls for greater democracy.
"That certainly is our position," Psaki said, adding that it had been communicated to China and that other issues would also be on the agenda. "There are certainly a range of issues on bilateral, regional and global issues that they will discuss during their meeting."
The United States has been carefully calibrating its response to the demonstrations, voicing support for non-violent protests, while signaling it has little interest in seeing them escalate and risk a harsher crackdown by Chinese authorities.
The official aim of Wang's visit, which also includes meetings at the White House and Pentagon, is to prepare for a summit between Chinese Premier Xi Jinping and U.S. President Barack Obama in Beijing in November, according to the Chinese embassy in Washington.
In a toughly worded letter to Leung on Tuesday, the chairman of the U.S. Senate's Foreign Relations Committee, Senator Robert Menendez, accused Beijing of "reneging on the promises it made to the people of Hong Kong."
"I write today to express my grave concerns over current events in Hong Kong," he said, urging Leung "to exercise your leadership to guarantee that your citizens, the people of Hong Kong, receive the full democratic rights and freedoms that they have been promised and which they deserve."
Senior U.S. military officials also made clear they were keeping an eye on China's response to the protests, and hoped it would not lead to a major crackdown such as the one 25 years ago when Chinese forces killed hundreds of demonstrators in Beijing's Tiananmen Square.
"Anything like that is concerning," Frank Kendall, the Pentagon's chief arms buyer, told Reuters in an interview. "A lot of us have memories of Tiananmen Square, and would not like to see that sort of a thing repeated."
China rules Hong Kong under a formula that accords the former British colony a degree of autonomy and freedoms not enjoyed in mainland China.
Any U.S. response could be a tricky balancing act, especially given Beijing's transformation into a global economic powerhouse and how inter-dependent the U.S. and Chinese economies have become since the Tiananmen crackdown in 1989.
On Monday, China warned against other countries interfering or "sending the wrong message" to protesters.
U.S. officials have steadfastly denied Chinese accusations of meddling in Beijing's internal affairs.
Obama is due to travel to Beijing in November for an Asia-Pacific summit and a meeting with Xi, and the White House said the U.S. leader was likely to raise human rights issues with his counterpart. (Additional reporting by Matt Spetalnick, Andrea Shalal and Patricia Zengerle in Washington; Editing by Jason Szep and Andre Grenon)