Vice President Bush's rivals for the Republican presidential nomination said yesterday that the snag in Moscow yesterday on plans for a U.S.-Soviet arms-control agreement and summit undercuts a major plank of his campaign, but Bush said they should not gloat prematurely.

With all the GOP aspirants focusing on next Wednesday's first debate, the vice president was being cast by his opponents as the spokesman for an administration stymied in its main diplomatic quest and defending a suddenly shaky-looking economy.

Former secretary of state Alexander M. Haig, one of Bush's five rivals for the nomination, commented yesterday that "if you take this {arms-control} problem and put it together with the growing lack of confidence in the economy, then it becomes clear the party can't win by offering more of the same."

Aides to three other GOP candidates -- Senate Minority Leader Robert J. Dole (R-Kan.), Rep. Jack Kemp (R-N.Y.) and former Delaware governor Pierre S. (Pete) du Pont IV -- all maintained that Bush had to be discomfited by his unqualified embrace of the Intermediate Nuclear Force (INF) agreement. Discussions aimed at setting up a summit meeting between President Reagan and Soviet leader Mikhail Gorbachev for the treaty signing suddenly broke down in Moscow yesterday when Gorbachev told Secretary of State George P. Shultz he wasn't ready to come to the United States until the administration accepted limits on its Strategic Defense Initiative.

Bush, campaigning in Iowa, said through spokesman Peter Teeley that "it is premature for political people to be saying the INF treaty will not go through."

Ten days ago, in his formal campaign announcement swing, Bush told an audience in Cedar Rapids, Iowa, that "we are on the verge of an historic arms agreement with the Soviets," eliminating the intermediate-range missiles on both sides of the Iron Curtain. Calling it "a new beginning," Bush challenged the other candidates in his party to "tell us where you stand."

When he spoke, du Pont, Haig, Kemp and Marion G. (Pat) Robertson had already criticized the impending agreement, citing what they called serious flaws in verification, concern over conventional force imbalance in Europe and other problems. Dole had announced he would reserve judgment until he sees the final terms.

Yesterday, they played "gotcha" with Bush. "It certainly makes clear why you shouldn't rush to judgment on a treaty that hasn't been written yet," said Mari Maseng, spokeswoman for the Dole campaign. "It has to affect George Bush," agreed Bob Perkins, her counterpart in the du Pont campaign, "because he wrapped himself around this treaty so thoroughly."

Charlie Black, a senior strategist for Kemp, said, "The one guy it hurts is George Bush. I wonder if he still thinks all the candidates have to sign on to this non-agreement."

Teeley said the other Republicans "should be careful not to be too gleeful. George Bush is not the only one who has pinned a lot on this treaty. Ronald Reagan, Margaret Thatcher and Helmut Kohl also feel it is very important."

Bush made the prospective treaty the centerpiece of his European trip earlier this fall and has mentioned it in almost every speech.

While others criticized or kept their distance, Bush endorsed it early. His advisers argued that Reagan's support of the treaty would minimize any conservative criticism and that Bush's efforts to make himself its chief promoter would emphasize what they call his "stature advantage" in the race.

Staff writer David Hoffman contributed to this report.