SAN FRANCISCO, JUNE 30 -- Leaders of the National Organization for Women (NOW), welcoming a surge of members alarmed by recent antiabortion rulings, today threatened a national boycott against a major European chemical company if it does not market its abortion pill in the United States.

NOW President Molly Yard, speaking here at a workshop at the group's 24th annual convention, said NOW representatives planned more discussions with the Paris-based makers of RU-486, the abortion pill now sold only in France. "If that does not break the logjam, we can come back and propose to everyone a boycott," she said.

Yard and Jennifer Jackman, a director of the Feminist Majority Foundation, indicated the boycott would target several popular products of Hoechst AG, the German chemical company that owns Roussel Uclaf, makers of RU-486.

The 2,000 NOW delegates here have focused much of their discussion on legal setbacks for abortion rights, including a recent U.S. Supreme Court decision allowing states to prohibit abortions for minors who lack parental or judicial consent. Membership in the organization dropped from 255,000 in 1982 to about 160,000 in 1988 after its effort to pass an Equal Rights Amendment to the Constitution failed, but a series of political and legal challenges to abortion rights have pushed membership back up to about 270,000, according to Sheri O'Dell, NOW's national vice president-action.

NOW leaders said they hope to use the membership surge to help elect candidates, particularly women, who support abortion rights. They are targeting governorships, where their candidates could veto antiabortion legislation. Patricia Ireland, NOW's national vice president-executive, said activist women also will be useful in any boycott against Hoechst, which owns the company that makes Celanese carpet fibers, as well as the Roussel Uclaf medical products firm. "Pharmacy schools are majority women now," she said.

RU-486, or mifepristone, can be used to abort embryos up to the seventh week of pregnancy and accounts for 33 percent of all abortions in France, according to Jackman. Antiabortion organizations have threatened their own boycotts if the pill is marketed here. "It's dangerous, a chemical coat hanger," said Kelly Connelly, a graphic designer who picketed today with about 50 other antiabortion activists in front of the convention's hotel.

Antiabortion groups persuaded Roussel Uclaf to take the pill off the market in France in 1988, but the French minister of health ordered it back into distribution two days later, calling it "the moral property of women."

Yard said the French company "totally freaked out" at the antiabortion pressure and interprets the 1988 election of President Bush, who opposes abortion, as a sign of widespread American distaste for RU-486. Yard also said the chairman of Hoechst is "an elderly man who is regarded as a very devout {Roman} Catholic and very close to the present pope." Pope John Paul II has been outspoken in expressing his own and Roman Catholicism's opposition to abortion.

NOW leaders said they expect delegates on Sunday to approve a resolution calling for an abortion-rights summit on ways to persuade Roussel Uclaf that the pill would be accepted in the United States. Ireland said marketing the pill may become easier if Hoechst, as rumored, decides to sell Roussel Uclaf.

Yard said the French firm also may want to license the pill for U.S. distribution to prevent illegal use without medical supervision. A woman using the drug takes three pills and two days later gets an injection of synthetic prostaglandin, which causes contractions that expel the fetus, Jackman said. Etienne Baulieu, developer of the pill, told a NOW group that serious complications can occur without supervision. They could result in legal problems.

Jackman said NOW should seek support from U.S. scientists and doctors for licensing of the pill. She said Hoechst was concerned about negative reaction to the fact that it once manufactured the gas used to massacre European Jews, but "we have to make it clear that it is essential to the lives of women to make this drug available."

The American Medical Association has called for marketing the pill, and California officials have suggested licensing it for sale in the state if federal officials are reluctant to approve national distribution.