Maryland Speaker of the House Benjamin L. Cardin, who is trailing two contenders in the campaign for governor, is expected to announce his political plans early next week, and most of his associates and potential opponents are betting that he will switch gears and run for the 3rd District congressional seat.

Cardin's intentions have been the focus of the state's political rumor mill in recent weeks, trading on what appears to be the increasing likelihood of Cardin's abandoning his statewide campaign.

Cardin, 42, has scheduled a news conference for Monday in Baltimore.

He will announce his intentions at a hotel located in the heart of the 3rd Congressional District.

"I've talked to a lot of people," he said. "It's been a very interesting process."

One source close to the Cardin campaign in Washington said: "Everything we have is that he's running for the seat."

Although his campaign for governor may not have taken off across the state, Cardin is a popular politician in his own district. When elected to be House speaker in 1979, Cardin was just 35, the youngest speaker in state history, and his leadership has been virtually unchallenged since. State politicians say he is a masterful legislative tactician and has built much of his strength in the General Assembly as a consensus politician.

Politicians throughout the Baltimore metropolitan area who had eyed the seat Democratic U.S. Rep. Barbara Mikulski is vacating to run for U.S. Senate already have begun to scatter at the mention of Cardin's name.

"I think when it all boils down, no one is going to waste the energy and time running for that seat" because they are convinced Cardin would win in the heavily Democratic district, said Baltimore City Council member Rochelle Rikki Spector, who had said she would like to run for the congressional seat.

And former Baltimore County Executive Ted Venetoulis, now a Towson newspaper publisher, said he was approached about running but rejected the idea. "My suspicion is that Ben is going to run for the seat," he said. The prospect of trying to succeed Mikulski "for a brief moment was tempting," he added, "but Ben has made the decision easy."

Cardin's talks in recent weeks have included Mikulski and Baltimore Mayor William Donald Schaefer, 64, who along with Attorney General Stephen H. Sachs, 51, is seeking the Democratic nomination for governor.

"I didn't want anybody at all in my campaign to indicate that we didn't want him to run for governor," Schaefer said.

But, he added: "He's got name recognition for that job that he wouldn't have had for another position; let me put it that way."

State Sen. Barbara Hoffman (D-Baltimore), who was appointed in 1983, said she too has heard that Cardin will run. Other Jewish candidates, she said, are especially unlikely to run against Cardin in a district that includes traditionally heavy-voting precincts in largely Jewish northwest Baltimore.

"We tend not to do that to each other," she said. Both Hoffman and Cardin are Jewish.

Old friends of Cardin, such as Del. Paul Weissengoff (D-Baltimore), have been clearing the decks for him. Weissengoff has paid visits to likely congressional candidates City Council member Timothy Murphy and state Sen. John Pica (D-Baltimore) to offer them words of discouragement about running against Cardin.

"I've spoken to a couple of people who are interested in running," Weissengoff said. "And I said if Ben Cardin is running I don't think you could win .

"I got the feeling they understood what I was saying to them."

Murphy and Pica said Cardin's prospective candidacy will not affect their decisions on whether to run. In interviews last week, Murphy indicated that he is still leaning toward running, while Pica indicated that he is leaning away from it.

"I don't think his election is a surety," said Murphy, a 35-year-old lawyer with Southeast Baltimore roots.

Pica, who has two small children, said that his forthcoming decision "has nothing to do with Ben Cardin. My decision rests on how a congressional campaign would impact a young family."

Like a house of cards, Cardin's decision to abandon his own House of Delegates seat has already caused what one political observer conservatively labeled "an interesting scramble" for the city's 42nd District delegate's seat.

Already, former delegates Steven Sklar and David B. Shapiro, who were squeezed out of their seats in 1982 after the area was redistricted, have expressed interest in returning to the House of Delegates.