President Carter, asserting that U.S. relations with the Soviet Union are improving, said yesterday that he expects to meet with Soviet leader Leonid I. Brezhnev for a "quite broad" discussion of overall Soviet-American relations that will not be confined to a new nuclear arms agreement.

"I think that in recent weeks there has been an alleviation of tension between us," the president said. "And I would like to see it continue."

Asked to elaborate during a breakfast meeting with reporters at the White House, Carter replied that "I can't say why" there has been a recent improvement in U.S.-Soviet relations.

He said the "low point" of relations during his administration came earlier this year during the trial of Soviet dissident Anatolly Scharansky but that "since then we have moved forward on better relations, a better understanding, more harmony and less disputes with the public media."

The president's assessment of American-Soviet relations was one of the most optimistic he has made, suggesting continuing progress in the strategic arms limitation treaty (SALT) negotiations. Carter said "every passing week" has produced the resolution of differences over a new SALT treaty.

It is taken for granted that Carter and Brezhnev, the physically ailing Soviet president, will meet to negotiate the final points of a new SALT pact and sign the accord. But the president yesterday stressed that he would not want such a summit meeting confined to SALT.

"I think at the time (of a meeting) we would be prepared to discuss, I hope, without any excessive time presure and with very good preparation, the broadest range of differences that exist between ourselves and the Soviet Union," he said.

On another topic, Carter said public financing of congressional elections would be "the best single thing that could be done" to dilute the influence of "single issue" groups in elections.

He called the more than $6 million that Sen. Jesse A. Helms (R.N.C.) spent to win reelection "unfortunate" and "excessive" and said members of Congress who accept large campaign contributions should ask themselves, 'Are we responsive to the general public, or are we excessively concerned with the intense lobbying pressure on this legislation?'"