Three days ago, Rep. Michael D. Barnes, a Montgomery Democrat, gathered a dozen of his closest political friends around him on a patio in Potomac to deliver a simple message. With a major family difficulty behind him, Barnes said, there was now no personal obstacle to his launching a campaign for a seat in the U.S. Senate.

The news delighted members of the group, one of whom said yesterday the 2 1/2-hour meeting ended "on two notes -- that Mike ought to run and that he could win."

"I'd back him to the hilt," said Morton Funger, a wealthy Montgomery County real estate developer and longtime fund-raiser for Barnes who hosted the meeting. "But obviously it's his decision."

Today, Barnes, 42, is at a crossroads unlike any other in his nearly seven years as the liberal congressman for Maryland's affluent 8th District. His House career has made him enormously popular among voters from Silver Spring to Gaithersburg, who returned him to office last fall with more than 70 percent of the vote. Barnes' position is a congressman's dream, a "safe" seat from which to rise to a senior post in the House, his allies say.

At the same time, Barnes is driven toward a race for the Senate by his own ambition and political forces inside and outside the state Democratic Party, supporters say. Friends also say the lengthy illness of his father, who died in July, made it difficult for Barnes to concentrate on his political future.

"Mike Barnes would dearly love to be a United States senator," said Judith M. DeSarno, his senior aide. "But there's a risk in running. Does he want to give up the House seat? Is the risk worth it?"

Indeed it is, say members of Barnes' inner circle as they watch the mating dances taking place among Democratic party leaders and Senate hopefuls such as state Sen. Stewart Bainum Jr. and U.S. Rep. Barbara Mikulski, a Baltimore Democrat.

Barnes' supporters said the right combination of money -- an estimated $1 million to $2 million -- and support from Baltimore area voters could give Barnes an edge in the Democratic Party primary next September.

The primary election would be considerably easier for Barnes, his strategists say, without the presence of Gov. Harry Hughes, an able campaigner who for months has devoted his administration's energy to resolving the severe financial crisis in Maryland's savings and loan industry.

"Hughes has lost some of his luster in Baltimore, regardless of what happens with the savings and loan crisis," said Gilbert B. Lessenco, a Democratic party leader in Montgomery. "Harry Hughes is holding back. My suspicion is that Mike runs."

Barnes' final decision, which he is expected to make within a month, also will be affected by any signals that incumbent Republican Sen. Charles McC. Mathias, 63, won't run. Mathias, who dissolved his reelection committee earlier this year, has not announced whether he will seek a fourth term. A spokesman said yesterday that the senator still has "an inclination" to run again.

In one sense, Barnes is behaving as if Mathias' decision did not matter. Like Mikulski and Bainum, Barnes is concentrating now on fellow Democrats by cultivating party leaders as diverse as Baltimore Mayor William Donald Schaefer; former state Sen. Harry McGuirk, the city's legendary political fixer; Lessenco; Montgomery County Executive Charles W. Gilchrist, an old friend who attended the meeting at Funger's, and Prince George's County officials. Barnes said in an interview last week that he intends to meet with Hughes shortly after the governor returns this week from a trade mission to Europe.

"The amazing thing is that very few party people are committed" to a candidate in the primary, said one Montgomery County resident who is close to Barnes. "It's the surprise of the season. For a state where peoples' allegiences tend to be intense, it's wide open."

Friends also say the death of John P. Barnes, the congressman's father, has nudged Barnes closer to a Senate run. "While his dad was ill, Mike was not able to focus on the politics of next year," said one Montgomery politician. "You put that together with so little activity on Mathias' part -- and with no signal from Hughes -- and Barnes has himself one hell of an opportunity."

A decision by Barnes to leave the House would almost certainly touch off a scramble among many Montgomery Democrats -- never ones to shy away from bitter primary fights -- to be his successor. Two millionaire politicians, Bainum and County Council member David L. Scull, have long coveted a seat in Congress and would lead a long list of other candidates for Barnes' job, party leaders said.

"It could set off a whole new 'What if?' game among us," cracked state Democratic Chairman Howard J. Thomas, a Montgomery lawyer. "And we Democrats love to play that game."