House Democratic leaders, expressing growing confidence that they can defeat a constitutional amendment outlawing desecration of the flag, yesterday denied a request by supporters of the measure to delay a showdown vote set for today.

In what appeared to be a tacit admission that their drive to persuade two-thirds of the House to amend the Bill of Rights is stalling, advocates of the flag amendment turned increasingly bitter as they pressed for a delay until next week.

Rep. Gerald B.H. Solomon (R-N.Y.), a leading backer of the amendment, took to the House floor yesterday morning and accused Speaker Thomas S. Foley (D-Wash.) of "kowtowing" to communists by refusing to postpone the vote.

"What you are doing, deliberately," Solomon thundered, "is gagging 10 million veterans throughout this nation from being able to mobilize and contact members of this House individually to put off the vote until next Tuesday. Mr. Speaker that is wrong. . . . I swear I just cannot understand why you cannot be receptive to the veterans of this nation when you are kowtowing to ilk like the Communist Youth Brigade and allow them to trample and desecrate our American flag."

Protesting the attack, angry Democrats later won a rare ruling from the presiding officer at the time, Rep. Jolene Unsoeld (D-Wash.), striking Solomon's remarks from the Congressional Record.

Democratic leaders, reminding amendment supporters that it was Republican advocates of the change, including President Bush, who had originally pushed for speedy action, turned down the appeal by lawmakers and veterans' groups for a delay. The key vote, which the House Rules Committee set for today, will follow five hours of debate on the House floor.

"This bill has been before the Congress for over a year," Foley said. "It has been debated and discussed as much as any other legislative proposal of this Congress."

As the House prepared to vote on the amendment, supporters conceded that the issue is not galvanizing the public as it did a year ago, when the Supreme Court issued the first of two rulings overturning laws banning flag burning as an infringement on the free speech protections of the First Amendment. If approved by two-thirds votes in the House and Senate, the proposed constitutional amendment also would require the approval of 38 state legislatures.

"People have just lost interest back home," said Rep. G.V. "Sonny" Montgomery (D-Miss.), a cosponsor of the amendment. "There isn't as much interest as a year ago, for what reason I don't know."

Montgomery, admitting that his side has failed to gain much ground in the past few days, said he is pessimistic about the outcome and believes the terms of today's debate will make it an uphill battle.

In sending the amendment to the floor yesterday, the Rules Committee also made in order another proposed statutory solution to the flag- burning controversy. That measure, which would make it a crime to destroy or damage a flag in a way that is likely to provoke violence, will be voted on after the proposed amendment.

Permitting another vote on a statute, Montgomery said, would give lawmakers political cover for opposing the amendment. "That weakens my position," Montgomery said.

Opponents of the amendment were upbeat about their chances of winning what has always been viewed as a tough election-year battle that GOP strategists have vowed to make an issue in the fall campaigns.

"We've got it," said Rep. Mike Synar (D-Okla.), claiming that amendment opponents are now being joined by some moderate and conservative Democrats from southern and border states. "These guys are beginning to see that it's not as big an issue as it was a year ago," Synar said.