President Carter's defense of his SALT II accord last night provoked only modest applause and cautious comments from a reserved and skeptical Senate.

Sen. Howard H. Baker Jr. (R-Tenn.), the minority leader, predicted once again that the new strategic arms limitation treaty "has no chance of being passed without amendment." Other senators yesterday echoed his determination to make alterations in the pact before voting to approve it.

A number of senators skipped last night's speech. Several of those president praised the address but also indicated that their votes would depend on more than the president's rhetoric.

Sen. Sam Nunn (D-Ga.), an infuential member of the Armed Services Committee and one of the senators the White House will court most ardently in the SALT debate, hailed the speech as "one of the best he [Carter] has made."

Nunn said he would not judge the treaty on the basis of the speech. Asked about the prospect of amendments, he said he couldn't predict his position on that question.

Another moderate of the sort Carter will need to win two-thirds approval for SALT II, Sen. Pete V. Domenici (R-N.M.), said the speech was "as forthright and positive as I've heard the president give." Domenici said that if he concluded the president's hopeful interpretation of SALT II was correct, he would vote for it.

Sen. George McGovern (D-S.D.), one of a group of liberal senators who have expressed dismay at the Carter adminstrations decision to develop a new MX supermissile while also pushing SALT, expressed the fear that Carter will "destroy hopes for real arms reductions" in the future by building big new weapons now.

An aide to Sen. Edward M. Kennedy (D-Mass.) expressed hope before the speech that Carter would include a pledge that the United States will not seek the capacity to wipe out Soviet missiles in a single strike, but the president chose not to include such a statement in the address.

Before Carter spoke last night, a leading critic of SALT II, Sen. Jake Garn (R-Utah), told a news conference he was drafting amendments to the treaty, and he predicted that SALT II will be rejected by the Senate "unless it is substantially amended."

Garn and several other Senate opponents of SALT II yesterday criticized Soviet President Leonid I. Brezhnev for his statement in Vienna that any change in the treaty might produce "grave and even dangerous consequences. . . "

Sen. Henry M. (Scoop) Jackson (D-Wash.) said of the Brezhnev remark, "they're already trying to do a little blackmailing" of the Senate.

According to well-placed sources, even Sen. Frank Church (D-Idaho), chairman of the Foreign Relations Committee, is looking for ways to alter SALT II by reservation, understanding or perhaps amendment. According to these sources, Church and his associates believe the Foreign Relations Committee will have to make some changes in the treaty to have any hope of influencing other senators.

Moderate and conservative senators who will hold the balance of power in the Senate debate - where a two-thirds vote is necessary to approve a treaty - seem particularly inclined to alter the pact.

For example, Sen. Daniel Patrick Moynihan (D-N.Y) all but declared his support for the treaty Sunday and predicted eventual Senate approval of it. But he quickly added that helping the president on SALT II "will involve putting some conditions and reservations on the treaty that can produce a two-thirds vote."

Carter and officials in his administration have taken just the opposite view, arguing that there is no room for significant changes in a treaty that took three adminstrations seven years to negotitiate.

However, senior officials acknowledge privately that the White House cannot take an utterly unyielding position. The challenge to Carter, as one source close to him put it, is to persuade the Senate - or a two-thirds majority - that any changes in the treaty requiring renegotiations with the Soviets would be unacceptable, while modest conditions or reservations might be tolerable.

Another problem, as administration sources observed yesterday, is the uncertainty on the American side as to how far the Soviets will be willing to go to accept Senate changes in SALT II. Brezhnev's statement in Vienna Sunday was imprecise and conditional - alterations "might" create problems, he said.

Even the harshest Senate critics of SALT II have declined to call for its simple rejection. Instead, they seem to be coming together behind proposals for substantial amendments or modifications in new negotiations.

Sources friendly to the new arms pact yesterday made available a detailed memorandum outlining a strategy to force the rewriting of SALT II apparently written by Richard Perle, an aide to Sen. Jackson.

The memorandum, written last January, proposes a "Motion to recommit" the SALT pact including a section of instructions to Carter on how it should be improved.

Those instructions say the treaty should give the United States the right to match the Soviet Union's 308 extra-large "heavy" missiles, should count as strategic weapons the Soviet intermediate-to-long-range Backfire bomber, should not limit cruise missiles in any way and should contain no provisions that cannot be "fully verified."

These changes amount to "killer amendments," according to Carter administration officials queried about them last night.

Sen. Jackson has been pursuing a strategy of changing the treaty for months. According to informed sources, he had approached the Repulican leader, Sen. Howard H. Baker Jr. (R-Tenn.), to discuss possible cooperation on some amendments. Baker, who has also spoke strongly in favor of changing the treaty, apparently wants to act on his own or with other Republicans, however.