Sen. Gary Hart (D-Colo.) yesterday warned liberals that the Democratic Party won't be able to capitalize on President Reagan's problems with female voters unless it stops treating women "as one more constituency to be placated."

In a sharp rebuke to his party, the Democratic presidential hopeful said women will stay away from the polls next fall or vote for a third-party presidential candidate unless the party makes "the full equality of women" its "principal interest."

Women have the power to elect the next president, "but that power will not translate into Democratic victory just because of what Republicans have done wrong," Hart said in a speech to Americans for Democratic Action.

Hart was one of three Democratic candidates yesterday to address the group, long a bastion of the liberal establishment. His remarks were seen as an effort to get out in front on women's issues at the beginning of a week that is to see the annual NOW convention and a Democratic women's leadership conference gather in Washington for heavy politicking.

In what aides described as a major policy speech, Hart said the Democratic Party "must share part of the blame" for defeat of the Equal Rights Amendment, failure to elect a single Democratic woman to the current Senate and widespread pay inequities among women.

Without mentioning any of his six announced opponents by name or offering specifics, Hart said "we have heard very little" during the presidential contest about women's issues.

"Can any of us say with confidence that our party has acted boldly on our commitment to the full equity of women?" Hart asked, adding: "It is not enough for candidates to say the right things before the National Women's Political Caucus of the National Organization for Women and then go back to politics as usual."

He proposed the party convene a conference to devise a strategy to ratify the ERA, reform pension laws that discriminate against women, make "the principle of pay equity a reality," and strengthen child-support enforcement. He also said the party should allocate half of its House and Senate campaign funds for female candidates next year.

Hart, whose campaign has been sputtering, tried to underscore his commitment to women by naming Rep. Patricia Schroeder (D-Colo.) as co-chairman of his campaign.

Former South Dakota senator George McGovern and Sen. Alan Cranston (D-Calif.) also sought support from the ADA yesterday. Former vice president Walter F. Mondale is scheduled to speak to the group Sunday.

McGovern, a former ADA president, outlined an eight-point program that he would implement as president. It included: withdrawing all American forces from Central America and Lebanon; killing the MX missile; reducing military spending; reviving the GI bill for today's veterans; a unilateral nuclear freeze; a major public jobs program; a revised farm program; and equal rights for women.

"I'm an unabashed New Deal Democrat," declared McGovern, the 1972 Democratic presidential nominee.

Speaking to the ADA by telephone from Maine where he was campaigning for support in a straw poll next Saturday, Cranston emphasized his commitment to negotiating a nuclear arms reduction.

"Lend me a hand in this campaign," he said. "It could be that together we can transform the world."

The ADA, which may endorse one of the Democratic hopefuls early next year, yesterday distributed a 58-page study of their voting records. It showed that Mondale, as a Minnesota senator, had the highest lifetime ADA approval rating, supporting the group's position 92 percent of the time.

The group rated Cranston 85 percent, McGovern 81 percent, Hart 79 percent, Sen. John Glenn (D-Ohio) 63 percent, and Sen. Ernest F. Hollings (D-S.C.) 33 percent.