Living up to its billing, the state Senate primary race between Democratic Sen. Margaret C. Schweinhaut and Del. Patricia R. Sher has emerged as the most clear-cut and fiercely contested battleground over abortion in Maryland this year.

Abortion has overshadowed all else in the bitter campaign leading up to Tuesday's Democratic primary in Montgomery County between two former political allies. Schweinhaut, a seven-term incumbent, was the lone woman senator to oppose abortion rights this year, while Sher, a 12-year delegate, helped lead abortion-rights advocates in the General Assembly.

With four days remaining, Schweinhaut, 85, is working furiously to shift the focus to issues other than abortion, and Sher, 59, is couching her position in the broader terms of protecting "individual liberty and the right to privacy."

Although abortion is a centerpiece in dozens of legislative races, the Sher-Schweinhaut contest provides the most stark contrast.

It matches two experienced lawmakers with similar overall records and philosophies, but polar opposite views on the most combustible social issue of the day.

Most political analysts in Montgomery say the race has tightened in recent weeks as voters have begun concentrating on the primary, and none is prepared to forecast the outcome in District 18, which includes Chevy Chase, Wheaton, Kensington and parts of Silver Spring.

Polls have shown consistently that sentiment in the district is heavily tilted toward abortion rights, which helps explain the strategies of the two candidates.

What remains unknown, political leaders said, is whether the issue will outweigh in voters' minds the residual goodwill that Schweinhaut has accumulated through 28 years in the Senate.

In the last few weeks, Schweinhaut has tried to move the race beyond abortion, attacking Sher for missing votes in the House of Delegates and calling her old ticketmate "derelict" in her Annapolis duties. Sher responded that Schweinhaut was "misinformed" or "lying" about her voting record.

Often the campaign has been marred by sharp exchanges and name-calling.

In a television interview, Schweinhaut compared a "one-issue" candidate -- a way she had described Sher previously -- to a trained baboon.

Although Schweinhaut emphasized that she was not specifically referring to her current opponent, Sher responded by referring to Schweinhaut as a "vicious old lady."

Recently, the Schweinhaut organization has raised questions about the operation and financing of a Wheaton tavern owned by Sher's son, prompting Sher to brand the accusations "unladylike."

One disinterested Montgomery officeholder called the race depressing but dismissed much of it is a sideshow. "There's really only one issue that divides them, and that's abortion," he said. Each has collected about $50,000 for the primary, which will decide who gets the Senate seat because no Republican filed in the district. Sher got $5,250 from abortion-rights political action committees and Schweinhaut got $1,000 from the antiabortion group Right to Life of Maryland.

Sher is one of three Senate candidates chosen for maximum support by the Maryland affiliate of the National Abortion Rights Action League, which hopes to shift enough legislative seats in the elections to assure passage of an abortion-rights measure next year.

One state senator from Montgomery described abortion as a "mega-issue" in the county. "We're not used to dealing with such things," he said. "Usually it's roads or something like that. It could bring out people who don't usually vote in off-year primaries."

Sher acknowledged that the role Schweinhaut played in the Senate filibuster in March, blocking passage of a majority-backed abortion-rights bill, is what prompted her to challenge a longtime political friend.

"But the longer I'm in it, the more differences I see," Sher said. "Maybe somebody should have done this 10 years ago."

Schweinhaut has portrayed herself as a staunch supporter of Montgomery's interests in the General Assembly, and points to her vote against construction of the baseball stadium in Baltimore, which Sher supported, as evidence of the difference between the two.

But, like it or not, Schweinhaut acknowledged that abortion remains the spotlight issue of the race.

"The press has kept the centerpiece as the abortion thing," she said. "And the nomination of {David} Souter to the Supreme Court has kept it stirred up and before the public. I don't think it's fair to me or the public."

Sher concedes that her race is grounded in her support for retaining women's access to abortions, but she says that endorsements from business, labor and police organizations reveal a broader base.

"These people don't care where I am on abortion," Sher said. "It says something about me and about my record." Schweinhaut said she counts on antiabortion voters and longtime supporters to make the difference on Tuesday. "People who I haven't been in touch with for 15 years are calling me and saying, 'We're with you no matter what,' " Schweinhaut said.

"We've created a lot of goodwill over the years. But what that means in terms of votes, I don't know."