Secretary of State Cyrus R. Vance said yesterday that any significant Senate amendments to the new strategic arms limitation treaty (SALT) would probably kill it.

At the same time, Senate Minority Leader Howard H. Baker Jr. (R-Tenn.) joined other senators in the judgment that SALT is unlikely to win Senate approval without meaningful changes of the sort ruled out by the Carter administration.

The exchange, on separate Sunday television interview shows, neatly summarized the administration's dilemma as informal debate over the treaty with the Soviet Union, concluded just last week, gets under way.

"This treaty is a very carefully crafted document," said Vance, appearing with Secretary of Defense Harold Brown on Meet the Press (NBC, WRC). "It is interrelated and intertwined and various parts of it bear upon other parts.

"Therefore, to amend any part runs a grave risk of killing the treaty completely. I can think of no real sunstantive change - in terms of an amendment - that wouldn't jeopardize the existence of the treaty."

Vance said that if treaty ratification fails, he believes it would not be possible to go back to the drawing boards with the Soviet Union and redraft an acceptable document.

The pact, to be signed next month in Vienna, requires approval by 67 of the 100 senators. The vote is already expected to be close, independently of the question of adding amendments to the treaty.

Baker, leader of the 41 Republicans in the Senate, said the Senate would be "actively engaged in the 'advise' part as well as the 'consent' part" in its consideration of the treaty-meaning he thought amendments would be plentiful.

Without changes, he said, it was "very unlikely" that the treaty would be ratified.

Baker, appearing on Issues and Answers, (ABC, WJLA), declined to predict his own vote, though he said he had "grave reservations," particularly about whether the arms limitations would be adequately verifiable.

Both Baker and Sen. Sam Nunn (D-Ga.), a key swing vote in the SALT debate, criticized President Carter's use of the word "warmonger" in support of SALT.

"We would be looked upon as a warmonger" if the treaty were rejected, the president said in a speech, "not as a peace-loving nation . . ."

Nunn said he thought the president was providing ammunition for the other side in the event the treaty is rejected. "I'd like the Soviets to at least go out and invent their own propaganda," he said.

Baker said he hoped the president could in the future avoid such "rhetoric" to characterize SALT opponents because it was "not a fair shake. If he continues," Baker said, "the treaty will be defeated" by the administration's own rhetoric.

Brown and Vance carefully avoided such phrases yesterday in their interviews, though their predictions of the consequences of treaty failure in the Senate were no less dire.

Vance said that it would not only "fuel the nuclear arms race," but could "even cause some unraveling" in the North Atlantic Treaty Organization and "put the severest strains" on the U.S.-Soviet relationship.

Brown said that, in addition to these results, failure of the treaty would mean that "other countries who now are restrained will be more likely to go ahead and employ their own nuclear weapons."

Brown also said he thinks there are "reasonable opponents" of the treaty, who fear that it could "lead to euphoria in this country which will cause us to assume that we don't have to have a strong defense." CAPTION: Picture, Secretaries Vance and Brown say amendments could kill arms pact with Soviet. AP