The State Department said yesterday that key members of Congress had been informed last month that the United States agreed to a one-year moratorium on new weapons sales to Taiwan.

Harvey Feldman, deputy director of the China working group, said Secretary of State Cyrus R. Vance had informed lawmakers in a White House meeting just before President Carter's announcement of normalization of U.S. relations with the People's Republic of China on Dec. 15. Presidential statements and a briefing for the press later that evening made no mention of the 1979 freeze.

A transcript of Vance's Dec. 17 appearance on CBS television's "Face the Nation" was produced by the State Department to show that the moratorium on new weapons sales had been disclosed.

Vance said at that time, "The arms to be supplied [to Taiwan] during 1979 will be arms which are already in the pipeline. In the post-1979 period we will be meeting new orders that come in..."

Officials said the United States agreed to the moratorium during 1979 at the request of Peking. The arrangement was described as something of a tradeoff for Peking's agreement that the U.S. mutual defense treaty with Taiwan could be abrogated with one year's notice rather than canceled out-right.