''There are times when we agree and there are times when we disagree,'' said Scott McClellan, a White House spokesman. ''The president makes decisions based on what he believes is the right policy for Americans.'' Mr. McClellan added that the ban was put in place as a way of deterring crime and that Mr. Bush ''felt it was reasonable.''

The White House position has heartened gun-control advocates. Matt Bennett, a spokesman for Americans for Gun Safety, which supports an extension of the weapons ban, said, ''I think Bush realizes that, number one, this is the right thing to do, number two, he promised to do this in the 2000 campaign, and number three, he knows that it's good politics and this is an extremely popular measure.''

The N.R.A. has maintained a polite civility toward the White House, even though it insists the ban is a violation of the Second Amendment that deprives hunters and sportsmen of many high-powered rifles.

Chris W. Cox, the N.R.A's chief lobbyist, said in an interview that while the defeat of the assault-weapons ban would be one of the N.R.A's top priorities, the group's focus would be on convincing members of Congress to vote against it so that it never reaches Mr. Bush's desk. ''Do we agree with the administration's position on this? No, we don't, but the real fight is going to be not at that level, but in Congress,'' he said.

A bill will be introduced in the Senate on Thursday by Senator Dianne Feinstein, Democrat of California, and Senator Charles Schumer, Democrat of New York, that would extend the ban for 10 years in much the same form it exists today. House Democrats expect to introduce a toughened version of the bill next week. That version, rejected by Senate Democrats as too politically risky, would significantly expand the class of banned weapons.

Mr. Schumer said he believed Mr. Bush's support could be critical in what he predicted would be a hard-fought campaign to renew the assault-weapons measure, which bans 19 types of firearms and others that meet certain criteria.

''We hope the president will not just say he supports the ban but will work to get it passed,'' Mr. Schumer said in an interview. ''This will be a good measure of the compassion in his compassionate conservatism.''