In one corner of the Maryland Senate office building here Monday was New Carrollton's Sen. Thomas Patrick O'Reilly, explaining to a handful of reporters why he was entering Prince George's County's special congressional election.

In the opposite corner was his colleague, Sen. Arthur Dorman of Beltsville, distributing a press release explaining why he WASN'T running for the seat, and "releasing any commitments for support from the many people he has talked to during the last three weeks." Back in the county, meanwhile, two of the other state senators ostensibly representing the people during this legislative session were out campaigning. Sen. Tommie Broadwater is cochairman of Steny Hoyer's race and Sen. Edward T. Conroy is doggedly pursuing his own dream of Congress.

That didn't leave much of Prince George's to watch the state Senate that day or through most of the rest of this year's General Assembly. But one can hardly be surprised.Late in a rather humdrum session and with a congressional seat in power-lovin' Prince George's suddenly up for grabs, perhaps it's only natural that half the county's legislators are dropping their committee meetings and plunging into the political action in one way or another.

Or talking as if they badly would like to. Del. Thomas Mooney, for example, has spent the last three weeks wistfully holding a wetted finger to the political currents here and wondering out loud whether he is in or out as a candidate.

At first he seemed to be in, but then Conroy -- like Mooney an anti-abortion and pro-veterans candidate, but one who enjoys more recognition -- announced his candidacy and Mooney talked himself down. That was before last week, however, when Montgomery Del. Stewart Bainum got into the race, frothing with the ambitions of the explosive young delegate once again.

"My God!" Mooney could be heard to shout across the crowds in the House of Delegates lounge. "Bainum's in the race and he's from Montgomery County. Why shouldn't I be there, too?" A crowd of sympathetic delegates would cluster around him and the appraisals and calculations of Hoyer, Conroy, Spellman and the rest would begin again.

Such colloquies are hardly out of place in the lounges and hallways of the statehouse these days, of course. The frantic scrambling for Prince George's open seat has been replayed as in a mirror here each day, not only by the legislator-candidates, but in a thousand different rumors and conferences and plots.

Legislative business? "What do you expect? We've got ourselves a campaign," answered one sensible delegate. And during a campaign, it seems, one must scrutinize every angle and watch all moves, especially when they come from opponents who join you every day in the same chamber.

O'Reilly is perhaps typical. Monday he began his announcement address -- delivered from behind his Senate office desk -- not with a platform or a slogan, but with an anxious question to the assembled reporters: "How about Ed Conroy -- has he pulled out?"

Conroy, of course, has been stopped outside the Senate to answer Annapolis rumors of his withdrawal so many times in the last two weeks that he has almost become convinced there is a conspiracy."I don't know how many times I have to answer these rumors, which are being spread by the Steny Hoyer crowd that wants me out," he says. "I'm in to stay, and anybody who doesn't think so is smoking something."

There are, of course, those who have chosen the high road. Del. Timothy F. Maloney, the blossoming young political strategist from Beltsville, began the campaign season trying to recruit a candidate for his "independent" Democrats to support and talked of abandoning the legislature for phone banks and leaflet drives.

Now, however, he settles for daily phone briefings on the race, between sessions of the House Appropriations Committee. "I've decided not to get involved," Maloney maintains, "because I think there ought to be at least one person sitting in the back two rows of the House chamber at the end of the session."

Those rapidly emptying rows, of course, belong to Prince George's.