"Every time anyone fires a popgun in the Persian Gulf," Senate Minority Leader Robert J. Dole (R-Kan.) complained in exasperation recently, "someone is going to want to invoke the war powers act."

Sen. Lowell P. Weicker Jr. (R-Conn.) pleads guilty.

But Weicker, as is his custom, puts it differently. The only issue, he says over and over again, is "whether the Congress of the United States is going to obey the law" by applying its war-powers constraints to U.S. involvement in the sharply escalating gulf hostilities.

For weeks, Weicker and a small, bipartisan band of senators have been pushing a reluctant Senate to invoke the 1973 War Powers Resolution, passed after the Vietnam war to assure congressional involvement in decisions that could lead to war.

They have neither won nor lost -- a familiar and not entirely discouraging situation for the maverick liberal Republican from Connecticut, who is a master of the politics of tenacity, skilled in the use of the power of shame and outrage.

Prompted by the news of a Silkworm missile attack on a U.S.-flagged Kuwaiti tanker, Weicker forced another test yesterday that resulted in an 89-to-3 vote against shelving the war-powers issue, the biggest margin so far in a series of procedural and test votes on the issue.

"When a missile hit a ship flying the Stars and Stripes, it is no different than a missile hitting this Capitol," Weicker asserted in bellowing tones that have marked debates over the years on issues ranging from Watergate to school prayer, the U.S. invasion of Grenada and privacy of an individual's tax records.

The vote had the effect of keeping the issue alive until Tuesday, when the Senate is scheduled to vote on a scaled-down version of the war-powers requirements that is sponsored by Majority Leader Robert C. Byrd (D-W.Va.) and Sen. John W. Warner (R-Va.), ranking Republican on the Armed Services Committee.

Weicker, who is among the most consistently liberal senators, is a minority within the minority, which is normally an automatic prescription for losing. He also lectures his colleagues on matters of conscience, principle and the Constitution, sometimes shaming them into votes they would rather not take.

His persistence has won out in the end on a variety of sensitive issues, contributing to eventual defeat of the New Right's efforts in the early 1980s to strip federal courts of jurisdiction over school busing cases, ban abortions and permit prayer in public schools. "Sometimes you just have to wear 'em down," he says.

As chairman and then ranking Republican on the Appropriations subcommittee responsible for health, education and other social welfare programs, he has joined with Democrats in trying to shield these programs from Reagan-era budget cuts.

But he has his share of losses, too. When the Senate two years ago approved the Gramm-Rudman-Hollings law to balance the budget, Weicker and a few others followed it up with proposals that would really cut the deficit, such as raising taxes, cutting defense spending and exposing Social Security to future cutbacks. They went down in flames.

Weicker is not new to the war-powers debate. He marched into the Senate in 1983 as it was showering the Reagan administration with praise for its invasion of Grenada, accused the administration of violating the law, the Constitution and assorted treaties and demanded that the War Powers Resolution be invoked. It was not.

He makes conservatives as well as liberals queasy by framing the debate in law-and-order terms. But they praise him nonetheless for consistency, perserverance and conscience.

"He's a man of tremendous courage to take positions in sharp conflict with the views of his party leadership and often the Senate as a whole," said Warner, who has gone toe-to-toe with him on the war-powers issue. "He's the conscience of the liberals," said conservative Sen. Charles E. Grassley (R-Iowa). He has "guts," said the more liberal Sen. Carl M. Levin (D-Mich.).

For Weicker, it is simply what the Senate is all about. "The pay is lousy; the hours are lousy. If you can't have the stimulation of fighting for principle, I don't want the job." His occasional victories "make it all worthwhile," he said. "I'll know when to leave, and it's not yet."