Constance A. Morella, a Republican who has represented Bethesda in the Maryland House of Delegates for two terms, opened a campaign for Congress yesterday that Montgomery County GOP officials called the best shot in nearly a decade to recapture Montgomery County's 8th Congressional District seat.

Morella, 54, an English professor at Montgomery College, announced her candidacy before more than 150 supporters in Rockville for what was once a solidly Republican seat, but the well-planned event went somewhat awry when she was confronted by an abortion foe, who demanded to know her position on the issue.

"Your record has been so perfect in voting for abortion funding . . . . Do you intend to change this so that you will not have the Gerry Ferraro problem?" shouted Kathleen Sweet, head of Right to Life of Maryland Inc., an antiabted bills in the Maryland General Assembly authorizing the use of Medicare funding to pay for abortions sought by poor women.

Afterward, Sweet said Morella would "have this issue hanging around her neck for the rest of the campaign," but Morella said she did "not believe that Montgomery County voters are single-issue voters."

Morella said she hopes to raise as much as $700,000 for the race and will campaign on social and economic issues such as balancing the budget, cleaning up the environment, improving health care and continuing federal funding for mass transit.

She also called for a "continuing dialogue" with the Soviet Union on arms control.

Michael D. Barnes, a Democrat who is running for the U.S. Senate, has represented the 8th District since 1979. But for almost 20 years before that the seat was held by moderate Republicans Charles McC. Mathias Jr., Gilbert Gude and Newton I. Steers.

Barnes defeated Steers in the 1978 election, and GOP leaders have been looking ever since for a candidate in the "Gude-Mathias mold" to win back the seat.

Yesterday, Morella made her ties clear. Her campaign chairman is Jane Gude, wife of the former congressman, who read a letter from Mathias pledging his "whole-hearted support" for her campaign.

"Connie has star quality and she is right smack in the middle of Republicans who have been successful in Montgomery County," said state Sen. Howard Denis (R-Montgomery).