WASHINGTON -- Two women's rights groups yesterday endorsed Philadelphia lawyer Alan M. Sandals for U.S. Senate, warning that abortion rights supporters may stay home this November if state Treasurer Robert P. Casey Jr. gets the Democratic Party's official nod to run against Sen. Rick Santorum.

Mr. Casey was recruited to run against Mr. Santorum by some of the most powerful Democrats in the country in the belief that his background as a conservative Democrat and staunch opponent of abortion would make him a formidable challenger for the two-term conservative Republican senator. And, so far, Mr. Casey is leading Mr. Santorum in the polls by double digits.

But Mr. Casey's opposition to abortion except in cases of rape, incest or when the life of the mother is at risk, in addition to his opposition to expanding federal funding for embryonic stem cell research and his support for conservative Supreme Court Justices Samuel A. Alito and John G. Roberts Jr., has created discomfort in some sectors of the Democratic Party.

Leaders of the National Organization for Women Political Action Committee and the Feminist Majority PAC said yesterday they are backing Mr. Sandals in the May primary because they want women's rights and abortion rights supporters to have more of a choice on issues they care about. In a February poll by Quinnipiac University, 53 percent of Pennsylvanians polled said abortion should be legal in all or most cases.

Kim Gandy, who chairs NOW's PAC, said the restrictive abortion laws just passed by the South Dakota and Mississippi legislatures have made it more important to build support for an abortion rights advocate like Mr. Sandals.

"Even the specter of a Santorum defeat is not excuse enough to betray our own rights," Ms. Gandy said yesterday.

Mr. Sandals, an attorney who specializes in pensions, said the Democratic Party's embrace of Mr. Casey was based on the "foolish belief that Democrats could win only if they began to impersonate Republicans."

"The consultants call this 'taking the issue off the table,' " Mr. Sandals said, referring to abortion, "but I call it ... political self-destruction." He said he believes much of Mr. Casey's support in the polls is merely name recognition, because Mr. Casey's late father had been governor.

But the Democratic Party's financial backing of Mr. Casey has created enormous financial hurdles for the lesser-known Mr. Sandals and the other Democratic challenger, Chuck Pennacchio of Bucks County, who also favors abortion rights.

Mr. Sandals reported in his most recent Federal Election Committee filing -- that of Dec. 31 -- that he had raised $23,693 in individual contributions, lent himself $125,842 and borrowed $400,000 for campaign expenses. At that time, the campaign had $50,230 in cash on hand.

Mr. Sandals declined to say yesterday how much he has raised since the beginning of the year.

Mr. Pennacchio had $9,078 in his campaign treasury at the end of last year.

By contrast, Mr. Casey had raised nearly $6 million by Dec. 31 and had $3.4 million in cash, compared with Mr. Santorum's $7.8 million in cash on hand.

According to Dec. 31 FEC filings, NOW's PAC had about $130,000 and the Feminist Majority PAC had less than $5,000 in its coffers.

Ms. Gandy said her organization would help Mr. Sandals through grass-roots activities and bundling contributions from the organization's members.