The day that the Rev. Jerry Falwell of the Moral Majority launched his crusade to kill the District of Columbia's new sexual assault law, the phone lines lit up in the offices of the House District Committee.

"It was unbelievable, we never saw anything like it before," said John Gnorski, minority staff director of the committee. "We must have gotten calls from staff people in more than 200 offices. And it was obvious that most of these people didn't even understand why the Congress was even considering a local D.C. law."

Those phone calls were the first signs of the intensive nationwide campaign by Moral Majority and other conservative Christian groups that this week led the House of Representatives to take the unprecedented step of overturning a local measure passed by the D.C. City Council and signed by the mayor.

But the calls also illustrate the congressional attitude toward the District which, many members and staffers said yesterday, made such a vote possible.

The lobbying against the sex law was undoubtably heavy and fierce -- Rep. Stanford Parris (R-Va.), for example, received more than 700 phone calls and letters from constituents demanding that he vote against the bill.

But that lobbying was only successful because most members have little knowledge of and pay scant attention to the affairs of a city that carries no political weight in their home districts.

If there are no gains for supporting the city in the face of constituent pressure, there is, as the Moral Majority's lobbying showed, a price to be paid.

"It's easy to take a shot at the District of Columbia," said Rep. Michael Barnes (D-Md.), a member of the District Committee who was on the losing side of Thursday's 281-119 vote to veto the sexual assault reform law.

"It's a no-loss vote for a member because their constituents don't care," Barnes said. "In this case, there was a fear by a lot of members that they would be seen to be voting in favor of sexual perversion. So what they did was take the easy way out, take the course of least resistance."

As a result, many members were reluctant to interpret the sex law vote as a sign that the Moral Majority had emerged as a powerful new lobbying force on Capitol Hill. This, said an angry Rep. Ronald V. Dellums, (D-Calif., chairman of the House District Committee, was a "cheap vote" to give Falwell.

"If you have groups in your district asking you to vote against something to do with the District, why should you go against them?" added one committee staffer yesterday. "They just wanted to get the Moral Majority off their backs. They didn't care one way or another about the District."

The degree of ignorance about District affairs in general and the sex law in particular was perhaps best illustrated during the course of Thursday's debate when Rep. Ronald Marlenee (R-Mont.) took the floor to launch a brief tirade about the city's soaring crime rate, noting that several friends from Montana had been recently mugged or robbed in the city.

"I'm mad about crime," he shouted. "I think it's time we tell the District to clean up its act."

Rep. John Conyers (D-Mich.) immediately interrrupted to ask Marlenee why the city's crime rate would be affected one way or another by the sexual assault reform bill then before the house. But before Conyers could finish, the burly Montanan had left the floor -- only to return hours later to vote against the sexual assault bill.

There were other factors that explain the overwhelming margin of the House vote. Some staffers blamed Mayor Marion Barry and District officials for failing to "do the legwork" necessary to explain the bill's provisions.

Others cited a growing congressional hostility toward the city brought out by a string of city-enacted measures that run counter to the prevailing conservative mood on Capitol Hill, including a voter-approved city-run lottery and numbers game and a change in hiring procedures for police ordered by Mayor Barry in an effort to increase affirmative action.Both of those actions were effectively nullified by the House.

"There are probably about 300 members of the House who are so fed up with the District right now that they'd vote against the city on anything," said Dick Leggett, an aide to Parris, who has spearheaded several successful efforts to nullify city actions.

Thursday's defeat leaves the city with a patchwork of antiquated sex laws including statutes, dating back to 1901, banning fornication, adultery, and sodomy between consenting adults. But there seemed little chance yesterday that the sex bill, which would have reformed those laws, will be revived any time soon.

Council member David A. Clarke (D-Ward 1), chairman of the Council's Judiciary Committee, who had worked hardest for passage of the legislation, was among the most embittered city officials yesterday.

"We'll let the dust settle," Clarke said. "But what does the Congress want us to do? I introduced this bill in the first place because the Congress asked me to. They asked us to pass it and so we did."

Clarke was referring specifically to the recommendations of a congressionally created Law Review Commission that had been forwarded to the council two years ago by the chairmen of two congressional subcommittees.

Those recommendations, Clarke pointed out, were virtually identical to the sex bill proposals that had been shot down by the House on grounds that it would have sanctioned homosexuality, sodomy and fornication in the nation's capital.

"What Congress tells us to do obviously doesn't mean a damn thing anymore," Clarke said. "I don't believe the Congress."