West German Chancellor Helmut Schmidt disclosed today that he has received a letter from Soviet President Leonid Brezhnev warning him against bowing to U.S. pressure to support anti-Soviet sanctions following Moscow's invasion of Afghanistan.

Anxious to keep his channels to Moscow open, Schmidt dodged questions at a news conference on whether Bonn will go along with a U.S. call to boycott the Moscow Olympics. But he said he did not consider the boycott as key issue in a Western response to the Soviet invasion.

Schmidt said, however, that following his recent trip to the United States, Bonn and Washington were completely agreed on all main issues arising from the Afghanistan crisis.

Schmidt added that the need to solve the Arab-Israeli conflict was becoming increasingly, urgent, and he said he would confer in Hamburg on Sunday with French President Valery Giscard d'Estaing.

Giscard recently completed a tour of Persian Gulf countries during which he publicly supported the Palestinians' right to "self-determination."

Schmidt refused to give details on the contents of Brezhnev's letter, but said it contained nothing to indicate a relaxation of international tensions.

Schmidt described the March 4 letter, a reply to one he sent Brezhnev in late January, as "moderate in tone but hard in content." He said it contained no threats but had a "warning undertone" about following the U.S. line in the current dispute with Moscow.

This Soviet refrain is an old one toward West Germany, but it has received heightened emphasis in recent weeks in the Soviet press and through Soviet diplomatic contacts here in an apparent concerted Kremlin effort to bring pressure on Bonn.

Keeping untroubled relations with Moscow is considered necessary by Bonn to maintain its policy of normal relations with Eastern Europe. At the same time, Bonn has sought since the start of this Eastern policy 10 years ago to assure America and the West of its allegiance to the Atlantic alliance and the European Community -- a point that Schmidt underscored again today.

While the Soviets are thought by Western analysts to have no illusions about being able to drive a wedge between Bonn and the West, they nonetheless continue to probe the relationship, apparently encouraged by stepped-up west German criticism of the United States and by the growth in Schmidt's own political strength in Europe.