U.S. Ambassador [WORD ILLEGIBLE] Toon today delivered a letter from President Carter to Soviet President Leonid Brezhnev and talked with him for more than an hour, chiefly about the growing possibility of a Soviet-American agreement on a new treaty to limit strategic nuclear weapons.

Their meeting was the first lengthy Tete-a-tete between Toon and Brezhnev since July, when U.S. Soviet relations were entering a chilly stage.

Tass, the official Soviet news agency, reported that Brezhnev spoke of "a definite change for the better in relations" between the Soviet Union and the United States.

The meeting especially emphasized "the urgency of finalizing the drafting of a new agreement on limiting strategic offensive arms" on the basis of accords reached in principle."

The agency did not explain further what "recent talks" it was referring to, in discussions that Soviet Foreign Minister Andrei Gromyko had with Secretary of State Cyrus Vance and Carter when Gromyko in the United States several weeks ago, Tass said. Those talks set off speculation in Washington and here that the two superpowers had charted general agreement on SALT II treaty.

In Washington, officials said Carter's letter to Brezhev, timed to the 60th anniversary of the Soviet revolution, dealt with "substantive" issues involved in the arms control talks, the negotiations on a total nuclear test ban, and other subjects.

White House Press Secretary Jody Powell said, however, that there were "no new American proposals on SALT or anything else" in the President's message.

An administration official said the letter was part of an expanding American-Soviet dislogue which "reflects the fact that there is more of a working exchange going on now". The administration also it wanted to expand Ambassodor Toon's participation in high-level exchanges, and that his hour-long meeting with Brezhnev served that purpose.

Although the Brezhev-Toon meeting touched off another burst of speculation that the SALT negotiations maybe near completion, administration sources said the anticipated completion date was sometime "early next year."

The interim SALT accord signed in 1972 limiting offensive strategic weapons expired Oct. 3, and the two countries have since mutually pledged to abide by its terms while seeking a follow-up treaty.

The Carter administration has briefed key Senators on the outlines of that accord, and it has already run into considerable opposition.

The speed with which the Carter letter was delivered and with which the meeting with Toon was arranged - coming as it did just the day after the Soviet Union's gals four-day celebration of its 60th anniversary - suggests an air of new courtesy and urgency in the complex negotiations.

Today's meeting was requested by Toon, who was accompanied by his political counselor, William Brown. Both men are fluent in Russian. Brezhnev, who met the Americans in his Kremlin office, was accompanied by his personal adviser, Andrei Alexandrov, and the longtime Soviet senior state interpreter, Viktor Sukhodrev.

The American Embassy, in a terse statement following Toon's meeting with Brezhnev, said the two men had "set forth their governments' position on a number of matters of mutual interest."

Carter's national security adviser, Zbigniew Brazezinski, recently remarked that U.S. - Soviet relations were "on the upswing."