Amid escalating warfare between arts supporters and religious conservatives, the fate of the National Endowment for the Arts may be decided this summer in a bruising House floor fight. Legislators on both sides agree that when Congress votes on whether to extend the federal arts agency's life for another five years, it almost certainly will impose restrictions on the content of works that receive tax-paid grants from the endowment. The furor began more than a year ago with criticism of NEA support for exhibitions of sexually graphic images by photographer Robert Mapplethorpe and artist Andres Serrano. In recent months, it has erupted in a barrage of emotional newspaper and radio commercials, letter-writing campaigns and court battles. Endowment chairman John E. Frohnmayer, caught in the cross-fire since he took office nine months ago, came under renewed attack last Friday when he overruled an NEA panel's recommendations and rejected grants to four avant-garde ``solo performance theater artists.'' The People for the American Way Action Fund, a liberal lobbying group, said Frohnmayer's decision ``has the smell of politics all over it'' and was intended to placate right-wing critics of the arts endowment. One of the rejected artists, John Fleck of Los Angeles, charged that ``there's a strong movement going on to wipe out different voices, to have a homogeneous voice that suits certain people's morals.'' Solo performer Rachel Rosenthal of Los Angeles reportedly refused to accept her $11,250 endowment grant, saying the four rejected artists were among the best in their field. ``Why should I be considered clean and they're considered dirty?'' she asked. Ms. Rosenthal also refused to sign a controversial pledge that she would not use endowment funds for obscene, indecent or blasphemous art _ a condition imposed by Congress last fall at the urging of Sen. Jesse Helms, R-N.C. Endowment officials say that of the 2,000 grants awarded so far this year, 670 artists or arts institutions have signed the agreement and received government money, 12 have signed the pledge with letters of protest and a half-dozen have rejected grant awards. The rest haven't yet responded. On the same day he rejected the four grants, Frohnmayer told an audience in his home town of Portland, Ore., that the stakes in the mushrooming controversy were high. ``A remarkable experiment that has lasted the last 25 years and has so enriched our country is indeed threatened with either extinction or severe crippling because of 20 images out of a million we have funded,'' he said. Frohnmayer, who opposes the Helms amendment, said the arts community must share the blame for the bitter controversy that imperils the endowment, an independent, $171-million federal agency whose arts grants must be matched by local private funds. ``We've acted much like spoiled children asking our parents to continue sending us money regardless of what we do, how we spend it or whether we are prepared to be held accountable,'' he said. NEA officials refused comment on published speculation that Frohnmayer might resign after the endowment's reauthorization bill passes Congress. When asked during his Portland speech if he planned to resign, Frohnmayer answered firmly, ``No way.'' Although no date has been scheduled for House action on the NEA bill, arts lobbyists expect a vote sometime before legislators begin their month-long summer recess in early August. Three or four major proposals circulating among House members include a conservative plan for severe restrictions on NEA grants and a major overhaul of the endowment that would shift a substantial portion of grant funds directly to state arts councils. Some conservatives favor abolishing the endowment. At the heart of the debate are conflicting arguments over the government's proper role in supporting the arts. The arts community and its supporters contend that restrictions on NEA grant recipients amount to government censorship. That argument is rejected by conservative lawmakers and religious fundamentalists, who say the real issue is the taxpayers' right to decide where their money is spent. The conflict is dramatized in toughly worded newspaper ads and radio spots sponsored by People for the American Way and its nemesis, the Christian Coalition led by evangelist Pat Robertson, who was a conservative presidential candidate in 1988. ``Do you want to face the voters in your district with the charge that you are wasting their hard-earned money to promote sodomy, child pornography and attacks on Jesus Christ?'' Robertson asked in a full-page letter to members of Congress that was published in The Washington Post and USA Today. People for the American Way put such performers as Colleen Dewhurst, Kathleen Turner and Garrison Keillor on the air to counterattack. ``Imagine a world in which millions of people are at the mercy of a small band of extremists, in which works of art are subject to government censorship and freedom of expression is a crime,'' said Miss Dewhurst. ``Now stop imagining. Welcome to America, 1990.''