Newton Steers sat at his desk in his study, far from the crush of the long campaign. There was welcome distraction in the quiet, and in the oak leaves tossing outside the window in the breeze. Mostly there was rue and resignation.

"I'm not going to cry about it," said Steers, at his home in Potomac. The day before he had been beaten by Democratic Rep. Michael Barnes in a race for the U.S. House seat from Montgomery County, a seat he had held two years ago and has sought five times in 20 years of public life. "I've won before and I've lost before," he said. "I'm not a little boy who cries when it all evaporates."

"He has a new layer to his carapace," said his wife Gabriele.

Campaign chairman Howard Denis wandered in. "I should have won it," Steers said.The phone rang with condolences. "It's the passing of an era," Denis said. "It's last hurrah."

For Congressman Barnes, Tuesday's 18 percentage point victory was a special triumph on a disastrous night for the party as a whole, and local Democrats promptly heralded it as the political confirmation of the 37-year-old rookie representative. For Steers, 63, it was perhaps the last time he would ever run for office.

Sitting in his brick-and-wood study with the ship's lamps on a desk, Steers said chances are "extremely remote" that he will try again. At the same time, he looked cheerfully to the future: an immediate vacation with his wife in the Caribbean, watching "uninstructive" TV shows, and the possibility of serving in the Reagan administration. But post mortems brought regret.

"I wish I had linked Barnes to Carter more," he sighed. "I should have pinned his clone to him, and hammered on the differences between us."

It seemed ironic to Steers and Denis that while Republicans nationwide were riding the Reagan landslide into office, the Republican momentum had the opposite effect in Montgomery. In the County, Democratic defectors to Reagan and perennial favorite Sen. Charles McC. Mathias (R), apparently felt obliged to split their tickets if for no other reason than to demonstrate their independence.

The race this year was dearer than the others for Steers because he had sought vindication. He lost in 1978 because he campaigned too cavalierly, certain of success, only to have Barnes edge him out by fewer than 5,000 votes in a dramatic upset.

This time, Steers threw his all into the race, announcing more than a year ago in October. During the last week, when the prognosis was grim, the candidate made massive loans to his own campaign -- more than $300,000. Staff members who sensed the defeat as early as three weeks before the end braced for what Denis called "black Tuesday," and tried to narrow the gap enough to leave "Newt" a measure of dignity.

When the end came (the vote was 140,214 for Barnes, 94,714 for Steers), many tears were shed, and campaign workers drifted around the Bethesda mall headquarters like mourners at a wake.

"We were running against a depraved charlatan," cried Gabriele Steers. A tart-tongued German, she had received her first glimpse of American politics, and she set down some notes on it, including the observation that "in this balkanized world of special interests and the need for kaleidoscopic knowledge of sundry subjects, it is quite conceivable that a politician may act politically intelligent and at the same time be a consummate nerd."

What anger her husband has, he says, is reserved for himself. "But I really meant it when I said I was more upset for the people who worked for me, Steers said. "One young man opened the office every morning at 8. It was his life. If I'm inured it's because I've lost before. I'm gratful for those who did so much to help me vindicate myself, but life goes on."