State Sen. J. Joseph Curran Jr. kicked off his 1982 campaign today, inviting friends and supporters to have coffee and doughnuts with him at the Knights of Columbus headquarters in the Northeast section of the city.

There was only one problem: no one in the room seemed to know what Curran was campaigning for. Though he is running for a fifth Senate term in his 43rd District, Curran's friends say that by this time next week he will be Gov. Harry Hughes' running mate.

Curran, 50, has been considered the front-runner for the lieutenant governor's slot on the Hughes ticket for three weeks. The job is open because Hughes announced last summer that he would drop incumbent Lt. Gov. Samuel W. Bogley from the ticket. Hughes wants a running mate from Baltimore to offset the strengths of the likely GOP nominee, Anne Arundel County Executive Robert A. Pascal. Now, with Hughes expected to announce his new choice by Friday, speculation was as common as the coffee and doughnuts.

But Curran and Hughes haven't talked for a week. Curran told one person after another this morning that he didn't know if he was on or off the Hughes ticket.

Speaker of the House Benjamin L. Cardin and Hughes discussed a Hughes-Cardin ticket last Sunday on the governor's yacht, but Hughes never offered the slot because Cardin would not guarantee that he would take it, according to informed sources.

"I'm still betting on Joe and giving 2-to-1 odds," said Del. Gerald J. Curran, who is candidate Curran's cousin.

Gerald Curran is waiting to see what happens, because if Joe Curran is tapped, his cousin plans to run for the vacated Senate seat. But he will not run unopposed. Del. John A. Pica Jr., also of the 43rd District, said he plans to run for Joe Curran's Senate seat if he doesn't run for reelection. "It has to be Joe," said Pica. "How can it not be Joe?"

Joe Curran, as he has done since his name first surfaced, played down his chances. "I'm sure they must be talking to other people," he said. "Right now, I'm running for the state Senate."

In fact, Curran introduced a united 43rd District ticket today. It included the two potential contenders for his seat, his cousin Gerald Curran and Pica, and four-term incumbent Democratic Del. Henry R. Hergenroeder Jr. But in their remarks, Pica and Gerald Curran pointedly said they hoped to return to "the legislature," without specifying which house.

"I asked him again this morning what he thought," said Joe Curran's younger brother, Bobby. "He said he didn't know, but he had this twinkle in his eyes. That's the most encouraging sign I've seen in a week."

That's the way it is for Maryland Democrats these days. A twinkle in the eyes might mean a political trend. Or it might not.