Thursday's shootings in Atlanta put renewed pressure on Congress yesterday to enact gun control legislation this summer and heightened fears among some Republicans that the changing politics of guns could leave GOP candidates vulnerable in next year's elections unless the party acts.

One day after Mark Orrin Barton shot and killed nine people before taking his own life with a gun, the House voted to appoint negotiators to work out differences with the Senate and produce a gun control bill before the August recess begins.

In doing so, the House urged its conferees to ensure that the legislation contains effective background checks to prevent criminals from buying guns at gun shows. But the language was vague, and a number of House GOP leaders remained resistant to some of the stiffer provisions of the Senate bill.

House Judiciary Committee Chairman Henry J. Hyde (R-Ill.) predicted difficult negotiations. "This is a very contentious and volatile issue and there are interests, diverse interests, tugging and pulling us in all directions," he said. "I expect this to be a difficult, but certainly not impossible, conference."

Republican ambivalence about how aggressively to move on gun control measures underscored the dilemma the party faces as it attempts to reconcile its traditional opposition to restrictions on gun ownership with growing evidence that key voter groups, particularly suburban women, want the government to do more to restrict the availability of guns.

Most independent and partisan analysts interviewed yesterday agreed that the politics of gun control appeared to change in April with the shootings at Columbine High School in Littleton, Colo., with more Americans supporting specific measures to restrict guns.

Andy Kohut of the Pew Research Center said his polling has found that gun control "has more kick to it" in the wake of Littleton. A poll conducted earlier this month described gun control as "the most explosive issue tested in this survey."

In that poll, 69 percent of those surveyed said that House members who vote for gun control should be reelected and 55 percent said that a lawmaker who votes against gun control should not be reelected.

"There is no question the issue is in transition politically," said Neil Newhouse, a Republican pollster. "It was crystallized more by Columbine, but I think Americans have begun to rethink their position on this issue."

Frank Newport of the Gallup Organization said strong majorities of Americans support such specific gun measures as trigger safety locks or background checks for people who purchase guns at gun shows, although he said his firm's polling has not found a significant change in opinion since the Littleton shootings. But Newport said Democrats have a clear partisan advantage among those Americans who want stricter gun laws.

Until relatively recently, the gun issue did not present a difficult choice for Republican officeholders. They generally sided with the National Rifle Association and other opponents of gun control measures because few of their constituents felt strongly enough about enacting stricter gun laws to make it a voting issue.

But with a spate of high-profile shootings at schools and other public places, the constituency in favor of more action to restrict guns has suddenly grown larger. "I think we're seeing, with incident after incident happening in the country, that that is leading to greater and greater concern about the issue," said Mark Penn, a Democratic pollster.

Kohut said the increased importance of the issue puts GOP lawmakers in a difficult position. "This is one where they have to be careful," he said. "One of the big shifts is among Republican women on the question of which is more important, to control guns or protect the rights of gun owners."

Many Republicans represent districts where opposition to gun control poses no risk, but for those in suburban districts, the politics of guns now demands some kind of response. "The Republican Party needs to do something," said Jan van Lohuizen, a GOP pollster. "Just exactly how much they have to do, I don't know. They're only on the wrong side if the answer is do nothing."

Newhouse also said Republicans can counter the Democrats' advantage on gun control by enlarging the debate to include other measures to reduce violence in movies and on television. "Democrats want to make this issue simply gun control," he said. "I think they fail to realize Americans believe it's about much more than guns and that's where the Republicans have the advantage."

Rep. Johnny Isakson (R-Ga.), whose district adjoins the site of Thursday's shooting and who voted for the Democratic version of gun show background checks, agreed that new gun laws alone are not the answer. "I think people are beginning to realize we're making a big mistake to make that the issue while all these tragedies go on," he said in an interview.

But as Republicans and the Clinton administration search for those other answers, Thursday's killings brought calls for quick action on gun legislation.

In June, the Senate passed juvenile justice legislation requiring a three-day background check on buyers at gun shows as well as language requiring the sale of child-safety locks with handguns and a ban on the importation of large-capacity ammunition clips. Later that month the House voted down looser gun control restrictions as part of its juvenile justice bill, so lawmakers must reconcile their competing versions.

Several top GOP leaders have worked to block stricter gun control. House Majority Leader Richard K. Armey (Tex.), House Majority Whip Tom DeLay (Tex.) and GOP Conference Chairman J.C. Watts (Okla.) all voted against instructing House negotiators on the question of gun show language yesterday.

The leadership also chose yesterday to appoint Rep. Robert L. Barr Jr. (R-Ga.), one of the House's most vocal opponents of gun control, to the conference. Rep. Rosa DeLauro (D-Conn.) said Barr's appointment showed the GOP's "lack of will to do what the public wills us to do."