A Republican candidate in Maryland's 1st Congressional District is making support for abortion rights the major thrust of his campaign -- a direct challenge to antiabortion forces within the party.

Raymond J. Briscuso, one of eight Republicans in the 1st District race on the Eastern Shore, is launching a television and radio advertising campaign in which he declares, "I strongly support a woman's reasonable right to choose" whether to have an abortion. "I think a woman, not a politician, should decide."

Rep. Roy P. Dyson opposes abortion, and one of his challengers, state Del. Barbara Kreamer, has made her support of abortion rights an issue in their Democratic primary.

Although Briscuso is not the only Republican in the 1st District race who supports abortion rights, his decision to base his campaign around the issue is rare. The GOP has officially opposed abortion in recent years, and the party's 1988 platform included an antiabortion plank. But Republicans who opposed abortion rights lost several high-profile contests last year, including the Virginia gubernatorial election.

Maryland's sprawling 1st District includes the Eastern Shore, most of Southern Maryland and part of Harford County north of Baltimore. It is predominantly rural and conservative, but a consultant to Briscuso said yesterday that a recent campaign poll shows a majority of the district's Republicans support abortion rights.

"We were shocked at the results," said Roger Stone, Briscuso's consultant. "This district is well to the right of the average Republican district, and we thought we would find that maybe 20 percent {of GOP voters} are pro-choice. Instead we found more than 50 percent are pro-choice."

The other Republican candidates who favor abortion rights are Wayne T. Gilchrest, a Kent County educator, and Talbot County lawyer Perry Weed. The other Republicans in the race are state Del. Richard F. Colburn (Dorchester); Calvert County Commissioner Mark Frazer; former Capitol Hill aide Luis Luna; Barry Sullivan, a Calvert County engineer; and Charles Grace, of Harford County.

Briscuso's ad campaign was designed by Republicans for Choice, a newly formed group seeking to counter the influence of abortion foes in national party circles. The group's chairman is Ann Stone, Roger Stone's wife.

Ann Stone said yesterday that her group endorsed Briscuso because its members believe he is the abortion rights candidate with the best chance of winning the GOP nomination and because they wanted to pick a race where the Democratic incumbent opposes abortion.

"This race is right here in the shadow of Washington, and if we can win, it will send a real strong message" to Republicans, she said. "If a pro-choice candidate can win in a conservative district, other pro-choice candidates can win elsewhere."

Briscuso had hired Roger Stone as his campaign consultant before the endorsement, a fact that Ann Stone said "makes it easier" to plan strategy for the campaign.

Roger Stone said that a poll of 1st District Republicans taken in early June found that slightly more than half support abortion rights. Recent polls taken by Mason-Dixon Opinion Research, a nonpartisan Maryland firm, had similar findings.

The Briscuso campaign poll also found that 22 percent of those surveyed considered a candidate's stand on abortion the most important issue in the race. Only concern for environmental issues rated higher.

Stone said that the Briscuso campaign has set up a telephone bank to identify Republicans who support abortion rights and will mail literature to them emphasizing that stand. Briscuso's television commercial on abortion rights will air near programs popular with women and young voters, those mostly likely to favor abortion rights.

Ann Stone said that Republicans for Choice is raising funds for Briscuso in several major cities. Roger Stone said that Briscuso's emphasis on abortion rights "allows him to tap into money that otherwise would not be there for him."

In the 1st District's crowded Republican field, Roger Stone said, none of the candidates has a strong geographic base and none is likely to get more than one-third of the vote. He believes that a strong turnout by abortion rights supporters could win the election.

But a campaign aide to Colburn said she believes Briscuso's strategy will fail. "Most people on the Eastern Shore aren't one-issue people," said Zanna Colburn, the candidate's wife. "If {Briscuso} is going to have his campaign on one issue, he's not in the mainstream of what most people are thinking about."