Virginia's two U.S. senators championed opposing sides in the Senate's gun debate yesterday, after each abandoned his earlier position on extending a federal ban on assault weapons.

The reversals by Sens. George Allen and John W. Warner, both Republicans, drew furious denunciations from advocates on each side and illustrated the powerful political crosscurrents in Virginia and across the country over what to do about gun violence and gun rights.

Warner co-sponsored an amendment to extend by 10 years the prohibition on 19 semiautomatic assault weapons, legislation he opposed when it cleared the Senate in 1994.

"Senator Warner has just aggravated gun rights people off the edge of the map. . . . There will be repercussions in the next election," said Philip Van Cleave, president of the Virginia Citizens Defense League, a 2,000-member gun rights group.

Allen voted against the ban, despite pledging during his 2000 campaign against then-Sen. Charles S. Robb Jr. (D) to extend the law and reiterating that support as late as last month.

"George Allen looked the people of Virginia in the eye and flat-out lied. . . . The only thing meaningless in the debate over assault weapons is his word," said Jon Cowan, president of Americans for Gun Safety.

Senate sponsors of a bill to shield gunmakers and dealers from lawsuits abruptly scuttled the legislation yesterday, after gun-control advocates added the assault weapons amendment by a vote of 52 to 47 and another amendment to require background checks for buyers at gun shows by a vote of 53 to 46.

Warner and Sens. Paul S. Sarbanes and Barbara A. Mikulski, both Maryland Democrats, voted for the amendments; Allen voted against them. All four then voted to kill the bill.

Senate Republican leaders also withdrew an amendment to repeal the District's ban on handgun ownership and other gun-control measures after the amendment's proponent, Orrin Hatch (R-Utah), said he had not had time to organize supporters.

Del. Eleanor Holmes Norton (D-D.C.) credited opposition by Police Chief Charles H. Ramsey, business leaders, residents and gun safety groups and appeals by District parents of children slain by gunfire.

"I believe we were persuasive that repeal of gun laws would be particularly dangerous in the midst of today's climate, rife with gang shootings and children shooting children," Norton said. Legislation to undo the D.C. laws remains pending in committee.

Warner and Allen defended votes that Allen called "the toughest since I've been here."

Warner cited Justice Department data showing that the proportion of assault weapons traced to crimes has dropped by 66 percent. He noted the support of the International Association of Chiefs of Police, the Major Cities Chiefs of Police and 200 sheriffs and police chiefs, including 25 from Virginia.

"I was persuaded by the law enforcement community," said Warner, who co-sponsored the extension with Sen. Dianne Feinstein (D-Calif.). "I'm thoroughly convinced the statistics do show a substantial reduction in use of these weapons in the perpetration of crimes."

Robert D. Holsworth, a professor of political science at Virginia Commonwealth University, noted that Warner has recently split with Allen over state tax increase proposals and other issues. Holsworth concluded that the spectacle of "dueling Republican Virginia senators" is evidence that "it's become increasingly likely there will be a challenge inside his Republican Party again if John Warner decides to run in 2008."

Allen cited police reports and federal felon surveys that show "so-called assault weapons" are used in only 1 to 2 percent of violent crimes. He said that popularly recognized weapons such as AK-47s and Uzi submachine guns are not covered by the ban, which draws distinctions among "hundreds and hundreds" of weapons with tiny variations.

"I recognize the symbolism of this to people on each side of the issue. . . . [But] if it's symbolic only, I'm going to stand on the side of freedom," Allen said.

Gun-control advocates attributed Allen's changed stance to his joining the Senate Republican leadership as chairman of the National Republican Senatorial Committee and said the flip belied his image as an ideological "straight shooter."

In the 2000 campaign, Allen appealed to moderate voters by embracing the assault weapons ban. As recently as Feb. 19, Allen wrote constituents that he would support extending the ban, saying, "I made a commitment to the people of Virginia."

Allen said that by switching sides, he took the tougher road. "I've always kept my word," Allen said. "I suppose the easy thing to do would be to say I'm for it, but then I'd be going against the evidence."

The National Rifle Association and allied groups have played a critical part in helping Republicans in congressional and presidential elections and have overtaken Christian conservatives "as the very best interest groups on the right at grass-roots mobilizing," said Quin Monson, assistant director of the Center for the Study of Elections and Democracy at Brigham Young University.

The NRA was the sixth-biggest donor to the National Republican Senatorial Committee in the 2002 elections, giving $411,000. Despite Allen's stance on assault weapons, the NRA ran more than 370 television advertisements against his opponent, according to Monson's group.