China and the United States announced today that Chinese President Li Xiannian will visit Washington next month at the invitation of President Reagan.

At the weekly Chinese Foreign Ministry press briefing today, a spokesman said other officials accompanying Li on the U.S. visit, scheduled for July 22, would include Vice Premier Li Peng, 57. The vice premier is a prominent figure in the leadership and is said to be the Communist Party's leading choice to become China's premier once Zhao Ziyang retires from that post.

One diplomat here said the addition of Li Peng, a Soviet-trained electrical engineer and China's leading expert on nuclear power, indicates that a visit to Washington, originally viewed as largely symbolic, is likely to be more substantive. The visit to the United States is expected to last about a week and will follow a state visit to Canada scheduled for July 14.

In March, the Chinese sent Li Peng to the funeral of Soviet leader Konstantin Chernenko, where he became the first Chinese official to meet Mikhail Gorbachev, the new Soviet leader. Gorbachev, at 54, is a contemporary of Li Peng. Li, no relation to the president, represents a new generation of technocrats being groomed to replace China's aging leaders.

President Li, 76, holds a largely ceremonial position in the Chinese hierarchy. A veteran revolutionary, Li has earned the reputation of being a survivor: He is the only member of the current Politburo Standing Committee not to have been purged during his career.

The symbolism of Li's visit to the United States is seen as important because it has the potential to help consolidate U.S.-China relations, which, despite recent snags, have been improving generally.

The postponement of last month's anticipated U.S. Navy visit to China revealed some of the ambiguities in bilateral relations. Chinese officials recently have been emphasizing differences with the United States over Taiwan.

But as one western diplomat said earlier this year, Li's visit to the United States should force the leaders and bureaucracies on both sides to move the relationship forward. It should show everyone that "the relationship is still working," said another western diplomat.

Moreover, Vice Premier Li Peng has the nuclear expertise to advance a long-stalled U.S.-China nuclear cooperation agreement. Li Peng could help resolve disagreement with the United States over nuclear nonproliferation guarantees if Peking wants to move in that direction.