The House of Representatives yesterday struck down the District of Columbia's recently passed sexual assault reform law, dealing what city leaders termed one of the most serious setbacks yet to the independence of Washington's six-year-old home rule government.

The 281-119 rejection of the measure marked the first time that Congress has overturned a locally approved D.C. law that had no apparent bearing on the so-called federal interest that theoretically gives Congress veto power over local legislation in the nation's capital. Action by only one house of Congress was needed to kill the bill.

The campaign against the measure was led by the conservative Moral Majority, which together with several local clergymen and citizens' organizations mounted a massive nationwide lobbying effort to repeal a bill that they said was a perverted measure that offended Congress and the American people.

The bill would have reformed the city's patchwork of sexual assault laws and legalized sexual acts between consenting adults, but its opponents focused on changes in the fornication, adultery and sodomy laws.

Yesterday's vote capped a series of defeats for the city in its relations with the Congress, including House action last week that effectively outlawed a police hiring plan ordered by Mayor Marion Barry, thwarted a city proposal to ship sludge to Pennsylvania and wiped out funding for a gambling lottery approved by city voters in a referendum last fall.

District officials and some of the city's strongest congressional supporters reacted with anger to yesterday's vote, denouncing it as a dangerous attack on self government in the city.

"I am outraged that Congress would not respect the local home rule process," Mayor Marion Barry said shortly after the vote. "It's setting a dangerous precedent for the Congress to overrule on a matter that has no federal impact and is not unconstitutional."

Rep. Ronald V. Dellums (D-Calif.), chairman of the House District Committee, had tried in vain earlier to have the measure of disapproval tabled on the House floor, then threatened to tie up the House for five hours of debate. But Dellums did not have the votes to prevail.

"It's very frightening," Dellums said later. "It shows that home rule is a total sham and a fraud, it's an outright lie. The city of Washington should walk down here and say either we're free or we're not. And if we're not, then repeal the Home Rule Act. That would at least be honest."

The vote was loudly cheered by the Moral Majority, whose leaders had sent out more than 800,000 mailing alerts all over the country urging its defeat.

Dr. Ronald Godwin, the Moral Majority's vice president, said it represented his group's biggest victory on Capitol Hill. He said congressmen feared public exposure by his organization if they supported the law, and he termed it "a victory for morality and common sense."

Godwin said the organization would continue to pressure the City Council if it attempts to pass a similar law. "We're not going to go to sleep, we're going to monitor this very closely . . . " he said. "You can expect that the next time something like this comes up, there will be people from all over the country in the council chambers."

While city officials criticized the Moral Majority for alleged fear tactics, local community organizations who opposed the law praised the congressional action.

"This is a great victory for grass-roots democracy against the oligarchy of the City Council," said Stephen Koczak, president of the Federation of Citizen Associations for the District of Columbia, one of the two principal citizen group coalitions in the city. The other, the D.C. Federation of Civic Associations, also was opposed to the sexual assault reform measure.

Koczak added, "We invited the Moral Majority in on this because the people in this city were opposed to it. We got 10,000 people to sign petitions that we gave to the Congress."

The bill was passed by the council in July after a week of emotionally charged debate among council members and in the city on the council's role in so-called moral issues and on a provision that effectively would have lowered the age of consent for sexual acts between children. That proposed change was eliminated, and Barry signed the bill.

The measure also contained sections that decriminalized homosexual acts, sodomy, fornication and adultery between consenting adults. It also allowed wives to press rape charges against their husbands, removed all references to the sex of the victim from assault laws, and lowered the penalty for rape from life imprisonment to 20 years.

That proposal had been recommended by women's groups who said it would make it easier to convict accused rapists.

The law, however, drew immediate fire from the Moral Majority, other Christian evangelical groups and The Most Rev. James A. Hickey, archbishop of Washington.

Resolutions to overturn the law were introduced by Rep. Phil Crane (R-Ill.) in the House and Sen. Jeremiah Denton (R-Ala.) in the Senate -- a procedure allowed for under the 1973 Home Rule Act, which permits either house to disapprove a council-passed bill altering the city's criminal code within 30 working days of its transmittal to the Congress.

The measure drew strong opposition on Capitol Hill, even though many of its provisions were identical to -- and in some cases less liberal than -- those in the home states of many of its congressional detractors.

During yesterday's debate, Crane called the bill "a substantial improvement" in the city's criminal code that was "unfortunatley laced with a handful of objectionable proposals that makes it totally unacceptable to most of the residents of the community and, more importantly, the majority of the people of the country."