These are heady days for Michael Barnes. Interviews on the Today show to tout his "war on drunk driving." Invitations to the White House to hear briefings on the president's Caribbean Basin policy. Informal chili dinners at Sen. John Glenn's Potomac home to discuss El Salvador.

The second-term Democratic congressman from Montgomery County has traveled fast and far from the lonely days of 1977 when his announcement to run for the congressional seat that Republicans had held for 18 years was greeted with the question, "Who the hell is Mike Barnes?"

The mild-mannered Barnes, with the look of man who might be teaching law on a college campus rather than writing it in the House chamber, upset the GOP incumbent in 1978 and now is moving to the head of his class in Congress. His unlikely rise is due in large part to the usual ingredients for success--ambition, hard work and political know-how. But Barnes' special talent for being in the right place at the right time hasn't hurt one bit.

No one is more aware of that than Barnes, who's taken to repeating a remark making the rounds on Capitol Hill: "If Mike Barnes were elected today to be chairman of a House subcommittee on swamps, tomorrow they'd discover that swamps contained the cure for cancer."

In three years as a congressman, Barnes has combined a knack for attracting lightning and an ability to harness it to gain the exposure usually accorded far more senior incumbents. It is all the more surprising because the bland and diligent Barnes does not seem the type to attract attention at all. But with his success, he has frightened off much of the competition in the usually fractious world of Montgomery politics, where ambition is never in short supply.

No one has appeared yet to challenge him in the September primary, and no one of note is expected to. The only Republican talking about the November race is the combative and conservative Montgomery school board member Marian Greenblatt. And while Republicans speak publicly about a "good shot" at wresting the coveted seat from Barnes, privately they tell a different story. "If we had a moderate Republican with lots of charisma," one party official said, pausing for dramatic effect, "well, then we still probably couldn't beat Mike Barnes."

The lightning first struck for Barnes when, as a rookie representative, he was tossed into the national spotlight by older and better-known Democrats. Seizing on the fading popularity of President Carter in July 1980, Barnes joined about three dozen congressmen to plot strategy to open up the Democratic National Convention to other potential nominees. The organizers decided to show their broad base of support by naming a younger member as one of their spokesmen. "So we looked around the room," one participant recalled, "and there was Mike."

By that evening, it was Mike Barnes' face on the CBS Evening News, Mike Barnes' office besieged by national reporters and Mike Barnes' home surrounded by camera crews. Two days later he was the guest on NBC's "Meet the Press," the result of another fluke.

The show's producer, Bill Monroe, was holed up in a country cabin on Saturday and needed to find a guest quickly for his Sunday interview show. He had the names of the "open convention" leaders, but no phone numbers. Monroe called directory assistance and found Barnes listed in Kensington.

At the time, Barnes was locked in a bitter election battle with Newton I. Steers, the millionaire Republican he had unseated in 1978. The next thing Steers knew, Barnes had beaten him by an 18-point margin to become the first Democrat from Montgomery to win back-to-back terms in the U.S. House in 40 years.

Within days of starting his second term, Barnes became the beneficiary of a palace revolt in the House Foreign Affairs Committee, where he served. Liberal Democrats staged an assault on the time-honored congressional seniority system, in which the main qualification for a chairmanship is length of service. They dumped the chairman of the subcommittee on inter-American affairs, which focuses on Latin America.

Democrat Dan Mica of Florida, also a sophomore but technically senior to Barnes by virtue of a coin toss, was next in line and thought he would get the job. "But a coalition of Democrats decided I was a bit too conservative, and I lost by one vote," Mica explained last week. "I hardly knew it was happening before it was over."

Barnes, who ranked next, was elected, becoming the first sophomore to chair a subcommittee in 30 years. Still sensitive to suspicions that he plotted for the position, Barnes says, "Yes, I was available and willing. But I did not initiate it. People came to me."

When Barnes ascended to the chairmanship, the subcommittee, in his own estimation, "was a backwater of foreign policy." Then El Salvador moved onto the front pages, and the 38-year-old Barnes moved with it, suddenly one of the leading Democratic spokesmen in the House on a prime-time issue.

The ever-cautious Barnes has remained in character with a delicate balancing act, publicly taking a mild anti-administration stance. "I think the United States should continue a modest aid to El Salvador, but the increases proposed by the administration are more than is necessary to achieve the limited objective our military program should have," Barnes said in an interview last week. "I'd like to see the proposals reduced."

Barnes, trying to play the role of peacemaker, has not joined the more strident critics who want military aid to El Salvador cut off. Instead, he would like to see Congress have specific control over any future military aid--taking from the president his current ability to increase aid under emergency powers without the approval of Congress.

By concentrating on such an issue, many congressmen would run the risk of alienating constituents interested in more parochial matters. But the well-heeled and well-educated voters of Montgomery County "like their congressman to be something special," according to one Republican on the Hill. "A national image gives him an extra measure of prestige."

Still, Barnes is not without detractors. They include a Democrat who questions his commitment to liberal causes and a Republican who insists Barnes is far too liberal for the 8th Congressional District. Pointing to the high vote ratings Barnes has received from Americans for Democratic Action, Republican state Sen. Howard Denis, who was Steers' campaign chairman, said Montgomery "is much more middle of the road than Mike Barnes."

Meanwhile, one longtime liberal commended Barnes for his position on the issues, then added that the congressman "is typical of those elected in recent years. What they do and how they do it is dictated by what's good for their careers. There is nothing particularly motivating them, other than how to get ahead."

Steers, twice defeated by Barnes, sees him as a "clever" man who won by misrepresenting Steers' record in Congress. As for Barnes' national exposure and its impact on the 1982 election, Steers is unimpressed. "John Brademas was beaten," said Steers, of the liberal House majority whip who went down in the Reagan landslide. "And he was heir apparent to the speaker of the House." What counts, said Steers, is "what has Barnes done for Montgomery County."

Barnes has managed to be at the forefront of one major local issue, the problems facing his large constituency of federal workers. He has done it without serving on the House Post Office and Civil Service Committee, an assignment chosen by most Washington area congressmen but not relished by the man from Montgomery.

"Some people still ask, 'Why isn't he on the committee?' " one aide noted. "Republicans snipe at him for not having to record his votes in committee on federal employe issues and then take the heat."

Instead, Barnes joined Rep. Vic Fazio (D-Calif.) in starting the Federal Government Service Task Force, which works on everything from fighting RIFs to battling the controversial transfer of a federal agency from Rockville to Atlanta.

No one who has watched Barnes in operation is surprised that he found a clever way to serve his constituents and his own distaste for a civil service committee assignment. For behind his mild demeanor is a skilled political tactician. Colleagues remember when Barnes went after a position as assistant majority whip--a post that offers access to the leadership and an insider's knowledge of strategy.

"Sure, some others wanted it, but their overtures came too late," said Rep. William J. Hughes (D-N.J.), the man who held the job before Barnes and left it for a higher post. "Mike said he was interested and tied down strategic support before some of the others even knew there was a vacancy."

Barnes has had plenty of practice in honing such political skills. Though virtually unknown to the public when he first ran for Congress-- one poll showed him with so little name recognition that his aides kept the depressing results from him--Barnes was no novice. He had worked for presidential candidate Edmund Muskie in the early '70s, organized a Democratic convention in Louisville that drew every presidential contender in 1975 to discuss the future of the party and directed the staff of the Democratic platform committee in 1976.

"Here was somebody active in party politics for 20 years," said Keith Haller, his former administrative assistant and longtime friend. "He knew more people in government when he came in than 99 percent of the congressmen who started with him. That's particularly helpful . . . when you have 435 congressmen all making requests and not everything can get done well on the other end."

Barnes seems to have done it all, without ever mussing his image as the staid Covington and Burling lawyer in the blue blazer, button-down shirt and rep tie.

"I think of myself as relaxed and easygoing, but not quite as serious and dull as I come across," Barnes said in a reflective moment last week. "Obviously I'm not flashy or strident. I don't think Montgomery would be comfortable with me if I were."

As this November's election approaches, Republicans casting about for a chink in the solid Barnes image are looking both enviously and hopefully to his prized press exposure on issues such as El Salvador. "He could go too far in becoming a national figure," said Maryland Republican Party chief Allan Levey. "That could be his Waterloo."

But most observers are looking past November to the next race Barnes might enter, and mentioning him as a potential candidate for the Senate, particularly if Republican Sen. Charles McC. Mathias decides to retire in 1986. "I have several people a day raise that question," Barnes said deadpan. "It comes up all the time, but I do not sit around and think about it."