Sen. Howard H. Baker Jr. (R-Tenn.), the minority leader, proposed yesterday that he be a broker in the Senate debate on a new strategic arms limitation treaty, mediating between President Carter and senators who want to make changes in SALT II.

If Carter would cooperate with him and permit the Senate to make significant but not crippling changes in the treaty, Baker suggested, he could support SALT II.

But if Carter adopted the position of Woodrow Wilson in the debate about the Treaty of Versailles and refused to consider substantive changes in the treaty, Baker said he would abandon the idea of cooperating with the White House.

With these remarks before the National Press Club yesterday, Baker set out the exquisite political dilemma he apparently hopes to pose for President Carter - either yield Baker a special role in negotiating changes in SALT II, or invite his opposition to it, thus substantially increasing the possibility that the Senate will reject it.

Baker insisted he did not favor "killer amendments" to SALT II but would support only changes that were "attractive and responsible." He did not specify what they might be, but Baker's previous comments have raised the possiblilty that his definition of "attractive and responsible" could conflict with President Carter's.

It was learned yesterday that Carter is considering making a major address on the treaty to Congress immediately after his return from the summit conference in Vienna where he and Soviet President Leonid I. Brezhnev wil sign the accord.

Although no final decisions have been made, it was learned that a speech to a joint session of Congress the night of June 19 is among the options being considered.

The president is to return from Vienna June 18 and leave the country again June 23 for a state visit to Japan and an economic summit conference with U.S. allies in Tokyo.

A speech to Congress would give Carter an opportunity to make his case for the treaty directly to members of the Senate, which must approve it, and to a television audience of millions. It would also capitaliz on public interest in the treaty generated by news coverage of the Vienna summit.

Baker said yesterday he realized that if Carter signals a willingness to negotiate changes in SALT II with all 100 senators, that would be "an invitation to the deluge," as he put it.Therefore, Baker said, Carter should "quietly" indicate a willingness to deal privately with him.

Baker revealed that he has already asked White House officials for a signal that they would be willing to enter negotiations with him on possible alterations to SALT II.

"I don't expect you to give me an answer now," Baker said he had told David Aaron, a senior foreign policy aide to Carter, "but I've got to have it soon." Baker said yesterday he is waiting for a reply.

Carter seems unlikely to jump at the chance to accentuate the role of a potential rival in 1980 in the way Baker proposes. But administration officials have acknowledged that Baker's support may be the key to winning two-thirds Senate approval for the SALT II

White House officials confirmed last night that Aaron and others met with Baker at his request to give him a briefing on SALT. Asked about Baker's request for private negotiations, these officials reiterated Carter's position that amendments to SALT II "are not necessary."

Baker said yesterday he does not yet know enough about the final terms of SALT II to declare his position on it. But he predicted flatly that the Senate would make changes in the treaty.

He charged that important aspects of the treaty are still not resolved, and said negotiators for the United States and the Soviet Union are now working feverishly to meet an early deadline - the June 15 summit - to complete the negotiations.

Baker listed items he said still had to be negoitated. They included the last items dealt with by Secretary of State Cyrus R. Vance and Soviet Ambassador Anatoliy F. Dobrynin before the agreement in principle on SALT II was announced last month.

Administration officials denied Baker's charge that important items remain to be negotiated. They said the current negotiations are intended to convert the last Vance-Dobrynin agreements into treaty language. CAPTION: Picture, SEN. HOWARD H. BAKER JR. . . . predicts changes in arms pact