A veteran Soviet propagandist made a sharp attack on AnWar Sadat today, declaring that the Egyptian president is searching for traitors to represent the Palestinians at next week's Cairo conference.

The strident denunciation by Yuri Kornilov, a longtime political commentator for the official press agency, Tass. ended the Kremlin's long official silence on Sadat's peace moves.

Meanwhile, high-level U.S. and Soviet diplomats were closeted at the Kremlin, reviewing the rapidly changing Middle East developments. The two countries chair the Geneva Middle East peace conference and have pledged to work together to reconvene it.

Under Secretary of State Philip C. Habib, who flew here last night, met with Mikhail D. Sytenko, head of the Kremlin's Middle East Bureau. Habib was accompanied by Ambassador Malcolm Toon, who last served in Israel and has substantial personal knowledge of Israeli Prime Minister Menahem Begin.

Habib, a specialist on the Middle East, is to leave Tuesday for Brussels, where he will meet with Secretary of State Cyrus Vance. Vance is heading for the Middle East next weekend.

An embassy spokesman said Habib's talks are "part of the continuing dialogue between the cochairmen nations of the Geneva conference." The spokesman conceded, however, that it was "unusual" for Habib himself to conduct the talks.

In his attack on Sadat, the Tass propagandist said the Egyptian leader "is searching hard in the Mideast and beyond, primarily in the U.S. for suitable candidates who could be rushed to Cairo and presented as some sort of representatives of the Palestinian people." Kornilov compared these persons to Quislings, the Norwegian traitors who collaborated with Nazi occupiers during World War II.

Kornilov labeled Sadat's assertion that he is seeking a comprehensive settlement "a lie a deliberate lie dictated by a desire to whitewash his separate deals with the aggressors . . . We are confronted here by Cairo's actual capitulation to imperalism, to militant Zionism. [This] is a betrayal, I repeat a betrayal of the Arab peoples of Palestine."

The Soviets have made support of the Palestine Liberation Organization a cornerstone of their maneuverings to exert influence on the peace talks, stalled since the 1973 Arab-Israeli war.