Just over two weeks ago at an 8 a.m. meeting, Prince George's Del. Lorraine Sheehan sat down with her friend and 5th District Congressman Steny Hoyer in his District Heights office. When each had drawn a cup of coffee, Hoyer gently told Sheehan what she had suspected for months: she was off the dominant Democratic ticket he once headed, despite eight years of his sponsorship, friendship and support.

"What Steny told me is that he would advise me to put out my own literature," said Sheehan, 45, a two-term delegate who is considered one of the most effective women legislators in the Maryland General Assembly. She later added, "I told him I was sorry to hear that because I thought he is a good congressman and I'm glad I've done what I've done for him--and I mean that."

With that, Sheehan said she considered herself officially on the outs with the rest of her district's legislative ticket, to be headed by state Sen. Bernard W. (Mike) Donovan, a fellow Democrat. Her ouster will force her to raise perhaps twice as much money as she'd planned and three times the $3,500 she spent in 1978. But Sheehan still doesn't understand just who engineered the fall.

Some of her colleagues blame Donovan for the move, citing longstanding conflicts between her progressive politics and feisty personality ("He's a chauvinist," says Sheehan of Donovan) and his conservatism and old-boy network allegiances. ("She's a women's libber and a pro-abortionist; I'm anti-abortion. We're 180 degrees apart," said Donovan of Sheehan.) Add to that Donovan's continuing fear that Sheehan would challenge him for his Senate seat.

Others feel she is being punished at the behest of Hoyer's friend and Democratic strategist Peter F. O'Malley for her intensive lobbying for the Branch Avenue Metrorail line, though many of Sheehan's fellow legislators deny O'Malley was involved. Most members of the Democratic organization support the more southern line ending at the Rosecroft Raceway, which O'Malley's influential law firm represents.

In any case, the incident again raises the question of the continuing influence of O'Malley and Hoyer in the Democratic organization they once headed, and the deep loyalties and expectations that continue to bind that group, even though the entity has been pronounced officially dead by the politicians who ran with the slate for years.

Sheehan, for her part, blames her fall from favor on what she will only refer to as "the pressure," and by that--though she won't say so--she means the wrath of one Peter F. O'Malley as a result of her two-year effort to see the Branch Avenue line built. "I can't think of anything else or any other reason," she said. "I'm Steny's handpicked person. . . . I worked hard to get on the slate. I worked harder to get on the slate than I did to win the election."

In Sheehan's first race in 1974, the slate meant that Sheehan's hard-won $10 and $15 contributions could be stretched to put her over the top. This time, with the advantages of incumbency, a strong record of advocacy for the mentally retarded and the support of women's groups, Sheehan still expects to make a strong showing even without the support of the ticket. But despite her confidence about reelection, Sheehan acknowledges that the fight with Rosecroft supporters has strained her relations with many Democrats who have friends on both sides of the issue. "I made a lot of people uncomfortable," she said.

The conflict began with constituent meetings organized by Sheehan two years ago, after the County Council voted to change the terminus of the Metro Green Line from Branch Avenue to Rosecroft, citing lower building costs and higher ridership. It escalated into a series of fiery leaflets and ads in the local and Baltimore newspapers, many of which implied that the decision to locate the Metro at Rosecroft was made contrary to the needs of the citizens. "They Think You'll Swallow Anything," was a typical line from a recent leaflet which Sheehan said she helped produce. The message continued, "Metro is now trying to aim the Metrorail line at Rosecroft to satisfy a few political interests . . ."

"One time Peter said to her, 'Why are you making this a personal issue, Lorraine?' " said a state delegate who considers himself a friend to both parties and thus asks not to be named. "She turned around and said, 'Peter, I needed you once but not anymore.' "

"The way we all feel about it was, we'd actually been close personal friends and political supporters," said County Council member Gerard McDonough, a Rosecroft supporter whose council district overlaps Sheehan's legislative area. "I went out and raised money for the ticket, and spent many a hot afternoon trudging up and down streets carrying literature for her--as she did for me. . . . It was just incredible to me that someone I considered my personal friend would lend herself to a slander on my personal integrity and honesty."

McDonough said the decision had less to do with O'Malley or Hoyer than with Donovan, who has never liked Sheehan and has looked for a way to avoid running with her for years. Her falling out with the rest of the old ticket merely gave Donovan an excuse to drop her, safe in the knowledge that no one would mind.

"It's an issue of representing my constituents," replied Sheehan, who denied having publicly slighted O'Malley or anyone else. "I think it's my job to represent what's in their best interests, or at least, what they perceive as in their best interests."

Donovan says that the decision on who he will run with has not been made, and will not be made until after the filing date, which was yesterday. He would have no comment on when or how he would make his decision. Hoyer was out of town at this writing and O'Malley could not be reached for comment. Though several senators, including the head of the delegation, denied that O'Malley and Hoyer had anything to do with the decision to drop Sheehan, Donovan was not one of them.

"It's not a one-person decision," he said. "You're either naive or new to reporting or don't know anything about politics if you think I didn't talk to Hoyer ." He acknowledged that strong feelings exist on all sides of the issue, and in a place like Prince George's, feelings do not have to be voiced to be considered. "You're searching for something I'm not going to tell you," he said.