The House easily passed legislation yesterday to weaken the 1968 Gun Control Act after adopting an amendment sought by the nation's police to continue the ban on interstate sales of handguns.

It was a resounding victory for the National Rifle Association, whose winning margin was widened by some lawmakers who privately admitted that they were sympathetic to police concerns but did not want to antagonize the 3-million-member gun lobby.

The bill would allow interstate sales of rifles and shotguns, ease record-keeping rules for gun dealers, allow dealers to make unrecorded sales from their personal collections, require evidence of "willful" violations in prosecuting dealers, restrict federal inspections of dealers and mandate minimum sentences for using a gun in a violent crime.

Law enforcement officials took comfort in their lone victory but did not hide their disappointment at failing to win other changes in the bill, which would lift restrictions on interstate transportation of rifles and handguns.

Final approval of the bill, sponsored by Rep. Harold L. Volkmer (D-Mo.), came on a 292-to-130 vote. NRA lobbyists said later they would seek to have the Senate, which approved a similar measure sponsored by Sen. James A. McClure (R-Idaho) last summer, 79 to 15, adopt the House version to avoid a conference.

Rep. Robert G. Torricelli (D-N.J.) called the outcome "a genuine disgrace. It's a classic example of the power of big money and a well-orchestrated campaign by a narrow interest. It's an example of the Congress at its worst."

But NRA spokesman Wayne R. LaPierre Jr. hailed it as "a major advancement" that addresses "the key problems law-abiding citizens have been having under the law."

Rep. Mario Biaggi (D-N.Y.), a former policeman, said the House had merely thrown "a bone" to police groups by voting, 233 to 184, to retain the ban on interstate sales of handguns. LaPierre said that amendment was unimportant to his group and has little effect on gun owners.

"The NRA cashed in all its chits on this one," said Barbara Lautman of Handgun Control Inc., referring to $1.4 million in NRA donations to congressional candidates in 1983 and 1984. But she said the vote on the handgun-sale amendment, offered by Rep. William J. Hughes (D-N.J.), "shattered the myth of NRA invincibility."

Hundreds of uniformed police descended on the Capitol to oppose the bill, but they were soundly beaten Wednesday when the House voted 248 to 176 against a Hughes amendment offered on their behalf. That amendment, besides retaining the ban on interstate handgun sales, would have banned silencers, barred unrecorded gun sales and maintained local restrictions on interstate transportation of firearms.

Several lawmakers attributed yesterday's outcome to the NRA's organizational advantage over police lobbyists, resentment at the House leadership for bottling up the Volkmer bill for seven years, and antagonism among many southern and western members toward gun control.

A leading western Democrat said he was among 30 House liberals and moderates who were privately embarrassed about voting against the police amendment to avoid angering the NRA. He said that had a priest been available, they would have "asked for absolution."

"We made the hard political calculus, 'Do I want to spend the next five months debating one crummy vote on gun control?' " this Democrat said. "The NRA's got the network, the head counts, they know who's wavering. The average deputy sheriff doesn't know a lot about how the House works.

"It's the kind of an issue that could defeat me when nothing else could," he said. "In a typical year, this is an issue in a Rocky Mountain district that could move 4 to 5 percent of the people to vote the other way . . . . If we cast a secret vote, the police chiefs would win today."

Biaggi said some Texas lawmakers told him they wanted to support the police amendment "but they have 300,000 members of the NRA in their districts."

Among the House members with liberal or moderate reputations who voted against the police amendment were Bob Carr (D-Mich.), Morris K. Udall (D-Ariz.), James L. Oberstar (D-Minn.), Dan Glickman (D-Kan.), Philip R. Sharp (D-Ind.), Gerry E. Sikorski (D-Minn.), David R. Obey (D-Wis.), Glenn English (D-Okla.) and John D. Dingell (D-Mich.), an NRA board member.

While the entire Massachusetts delegation and 13 of 14 New Jersey members voted for the police amendment, it was opposed by the entire Mississippi, Louisiana and West Virginia delegations, 22 of 27 Texas members and eight of nine from Tennessee.

The widely differing perceptions of one provision, which allows transportation of unloaded, "inaccessible" firearms across state lines, was typical of the debate.

To Rep. Roy Dyson (D) from Maryland's Eastern Shore, the provision made him think of his brother's wife. He said she carries a gun for protection in her rural area, and he wondered whether she might be arrested on a shopping trip to Virginia.

"I'm fundamentally opposed to gun control," Dyson said. "I represent my district on that. My cousin and sister-in-law keep guns. All my life, we've had to deal with snakes coming up on the porch, and wild dogs. We feel very comfortable with guns. I don't think urban legislators understand that."

To Biaggi of the Bronx the same provision conjures up criminals speeding down interstate highways. "What does 'inaccessible' mean?" he asked. "You put a gun in a glove compartment, how long does it take to put a clip in it? Five or ten seconds?"

Dyson also said that Judiciary Committee Chairman Peter W. Rodino Jr. (D-N.J.) "misjudged the strong feelings on this issue" by not producing an alternative bill until Volkmer's allies had gathered nearly enough signatures on a discharge petition to force their measure to the floor. "I had had it up to here," he said.

On the other hand, Rep. Stanford E. Parris (R-Va.), who signed the discharge petition, voted for the police amendment.

"I'm a gun owner, I hunt . . . . But I thought those were legitimate law-and-order concerns," the Alexandria lawmaker said. "I just don't know too many people who go hunting with a silencer on the end of their gun."

Torricelli said many members fear the kind of campaign the NRA mounted against him in his first congressional race in 1982, when his Hackensack district was flooded with mailings accusing him of wanting to take away people's guns.

"The NRA has been investing in this for years and it just paid dividends," Torricelli said of the vote. "If I sound bitter it's because I am."

Some police officials reacted the same way.

Gary Hankins of the Fraternal Order of Police in the District urged his members to drop their NRA memberships because of the "dangerous" bill.

Hubert Williams, president of the Police Foundation, said that "some congressmen were genuinely afraid" of being placed on the NRA's "hit list."

NRA spokesman John Aquilino said, however, "The few people that are claiming to speak for the police obviously don't." He said many rank and file officers supported the bill.