You remember the words to that song: ". . . Last night you opened and there your are. Next day on your dressing room they've hung a star. . ."

Well, nobody actually hung a star on Rep. Michael D. Barnes' Longworth Building office door Monday morning, but except for that, and a few other details, the story's the same:

Local congressman (or actor, author, quarterback, flagpole sitter) catapulted to stardom overnight!

The approving phone calls were still coming in yesterday at the rate of about one every 15 seconds in Barnes' office. And that was, the staff said, nothing compared to Monday.

Because just before the weekend, the Maryland Democrat announced that he and a group of some 40 congressional colleagues were going on record calling for what has become known as an "open convention" for the Democratic Party next month in New York.

Barnes is a freshman from Montgomery County, Md., where it's been said that they like their congressmen to be like the fifth man in the car pool -- no jokes in the morning, no cigars and his wife never needs the car on his day to drive. In other words, dependable and liberal-sounding and maybe a little bland.

Barnes is certainly preceived as dependable, but if the initial reaction to his startling move Friday -- and his subsequent appearances on the Big TV News shows ("Meet the Press," "CBS Morning News, among others,) -- is indicative, Montgomery County may be losing its taste for bland.

Mike Barnes can't exactly remember when he first started feeling that something had to be done. He says he's been hearing that sentiment voiced at campaign functions for weeks. "People kept asking me what I think should happen and my response just evolved into 'I think there should be an open convention.'"

"There is," said Mike Barnes, "a tremendous frustration in Montgomery County with the possible choice of Ronald Reagan or Jimmy Carter, which is evidenced in part by the great popularity of John Anderson in Montgomery County. I don't think it's related so much to Anderson qua Anderson," said Barnes, "as it is Anderson qua he's-not-Carter-or-Reagan."

Of course, John Anderson looks like a perfect fifth man in anybody's car pool, just the kind of liberal-sounding Republican type Montgomery Countians have always liked to send to Congress, although not necessarily to the White House.

Mike Barnes also meets most of Montgomery's Congressional Criteria: He is slim, moderately tall, with moderately fashionable gold-rimmed spectacles on his moderately patrician nose. He is wearing a blue and white striped shirt with a blue and white dotted tie. He is a lawyer and studied international economics.He was in the Marines, served on the Maryland Public Service Commission, is married and lives in Kensington with his wife, Claudia, and two daughters, ages almost 5 and almost 1.He is moderately good looking, very intense and as protective of his family as a congressman can be whose constituents are a phone call away and who lists his number in the phone book. He points out with some pride that two of the three top jobs on his staff are filled by women. He has built a reputation as a "solid," liberal legislator and he pays close attention to constituent service.

Most voters in Montgomery are registered as Democrats -- about 2 to 1, but they often vote for Republicans. There is a small but growing group of voters that simply "declines" to list a party preference. But by large, the county votes for what the voters see as "good government." "Moderate" is the ultimate compliment for a politician of any party. And as often as not the appearance of moderation is more persuasive than the fact of it.

If Barnes is reading his constituency well -- and the local mail and phone calls, he says, tend to support it -- Montgomery County simply doesn't want to vote for Reagan and can't make a case for supporting Carter.

Others see less selfless motives in Barnes's action. Barnes' Republican opponent is former congressman Newton Steers, who was unseated by Barnes two years ago. His assessment of Barnes' current stance: It's a sign of desperation.

Montgomery County's affluence is legend as it beats out, with some regularity, one or two other counties in the country for the distinction of highest median income. It has a large, mostly professional Jewish population and is full of academically oriented public high schools, pumping out college-bound achievers by the hundreds every year. Its property values have been out of sight for years now, and it is dotted with parks, golf courses and private and community swimming pools.

Mike Barnes, sitting back in his congressional swivel chair, the bright summer sun breaking through the mini-slatted blinds and lighting his somewhat tired-looking and not a bit tanned face, is not surprised at all to hear that swimming pool chitchat this summer has been concerned with dreaming up dream tickets. (Like Muskie-Jackson. Or Mondale-Jackson. Or Mondale-Muskie.)

"I think," says Barnes, who feels "sobered" by both the responsibility and the publicity, "I think that we're trying to save the Democratic Party."

Ironically, he says, it's the same thing Carter tried to do in 1972 when then-Gov. Carter led a stop-McGovern movement, which Barnes supported.

"Carter was arguing that McGovern would go down to disastrous defeat, harm the Democratic Party and lose good Democrats in the House and Senate. . .Our position today is very similar except that Carter today looks like more of a potential disaster for our parter than McGovern looked like then."

Mike Barnes, who will be 37 years old in September, says he hasn't slept very well the past few nights worrying about the responsibility and awed by the enormity of the party revolution in which he has such a key role and the extent of the response.

He worries that the intent has been misunderstood. "We don't seek to tell delegates who are committed to Carter they can't vote for Carter." Instead he said, he and his 40 or so congressional colleagues and others who will today merge into a national organization are simply trying to head off a proposed rule that "would threaten a delegate that if you step out of line or something we can just remove you and replace you with a more loyal delegate.'"

"You know," he recalled, almost wistfully, "it as just so offhanded at the meeting. Somebody said, 'Well Mike, and Don [Rep. Don Edwards (D-Calif.)], why don't you be spokesmen'. . .and I walked out of the meeting and the world. . .the sky fell in."

Mike Barnes called his staff together yesterday to thank them for bearing up under such a load. But he says he suspects the one enjoying it most is his press secretary, Bill Bronrott. Said Barnes, "You know, here you're six months out of University of Maryland journalism school, you get a job with an obsure freshman congressman and the next thing you know you've got all your heros lined up out there."

The center of open-convention action moves away from Barnes' office today with the announcement of the opening of a national office with Washington attorney Edward Bennett Williams as its chairman. Another office will open in New York in a few days. But for the time being, the mythical star is still on the Barnes office door.

On the Barnes office wall there is an autographed picture of longtime friend and mentor Robert Strauss. Strauss and Barnes worked together on the 1976 party platform. They've spoken recently, says Barnes, and he listened to Strauss' position.

The inscription on the picture starts out ". . .with deep respect and admiration. . ."

"Well," says Barnes softly, "I'm not sure he'd say that now. . ."