Wasn't it Scott Fitzgerald who said there are no second acts in American lives?

Dan Brewster leaned back from the newspaper-covered picnic table on the lawn between the pool and his sprawling country house. His hands clear up to the wrist were freckled with green sauce from the crabs he was eating. One eye always on his wandering 7-month-old daughter Danielle Lynn, he was listening to a report on a sick colt. Its temperature was down to 100 now, he was told. Great. This morning he'd given it a shot of penicillin.

Farther down the table his teen-age stepdaughter was arguing with her friends about whether to go see "Revenger of the Pink Panther" or "Foul Play," and his third wife, Judy Lynn, was trying to get everyone to move to the patio because the string beans were ready ("picked this afternoon") and the corn and fried chicken, and besides it was thundering and Rabbit the near-Labrador was getting frantic.

Those who knew before say Daniel Baugh Brewster is a different person today, Born to wealth, tall and handsome, he was president of his class in college, captain of the football team, at 19 the youngest officer in the entire Marine Corps, at 26 one of the youngest Maryland state legislators ever, a U.S. Senator at 39 . . . people called him Golden Boy.

"It all came so easily," he said.

And in 1968 it all came to pieces.

The drinking got out of control. He lost an election to his old college friend Charles McC. Mathias. He was divorced, nearly died the following year after an alcoholic collapse. And then there was the federal indictment, "something I didn't understand and still don't understand." In any case, it broke his career.

"Alcohol began to be a problem in the Wallace campaign of "64," he said, going back to the time when he ran in the Maryland primary for president as a stand-in for Lyndon Johnson to test George Wallace's strength. It was a hard race. He barely won.

For the next four years, though there were long periods of sobriety, the drinking gradually took over. He tried every dodge he could think of: not before 5 p.m., not after 5 p.m., only in Washington, only in Maryland, only at meals, never at meals, and so on.

By 1969, after the defeat for re-election to the Senate - Republican Mathias used a slogan that hurt by it very diffidence, "Reason for Change" - Brewster was "drinking with a vengeance," as he put it.

He didn't get really turned around until 1973.

"First you have to admit to yourself that you're powerless over alcohol. It's a drug, and the alcoholic is an addict, it's as simple as that. You turn over your life to it, and then you go step by step. It's not instantaneous, you don't achieve independence in one day. In my own case I came back (to the sanitarium) several times. I got my master's and doctor's degrees.It took a promising career, and it takes a long time to rebuild a life."

Dan Brewster says he has learned to roll with the punches and accept life on its terms. This from a compulsive achiever who won his first 12 elections, from the House of Delegates in 1950, the year he got out of law school, to the Senate in '62. . .

He was the oldest of six, and his father died when he was 10. Raised in comfort on a beautifully appointed farm in Maryland fox-bunting country, inheritor of the Baugh Chemical fortune, he altzed through St. Paul's School, started at Princeton and when war came enlisted in the aMrines as a private.

Next thing he knew, he was an officer leading assault team onto Pacific beaches, collecting seven wounds and a chestful of medals (on Okinawa his Raider unit was point for the initial attack and he personally, his own personal body, was point for the unit), coming home a captain. He retired a colonel in the reserves in 1972.

"The Marine years were my most formative years," he said. "I went in a sheltered kid, and at 21, I was a company commander. I came out of the war with a very different sense of values: I was interested in civil rights, politics. Really admired FDR. I joined the American Veterans Committee for awhile. Things happen fast in a war. You stop being a schoolboy in a hall of a hurry."

The military experience influenced his thinking in another way too: For years he was the most hawkish of hawks on Vietnam. "Let's face it, I was always a hawk. I wanted to go in there and do the thing right if we were going to do it all. Even drop the bomb."

This was, he added, the greatest mistake he ever made on a public issue in his decade in Congress.

"I went over and saw the soldiers, I was given the tour, and I saw that people were getting killed because we didn't have an all-out commitment there.I used to say, if it was worth doing. The fact is, it wasn't worth doing in the first place. Being a world leader doesn't mean you should police the whole world too."

But the issues of world affairs can seem abstract to a man living close to the earth. (And he does that, even if it is a model 150-acre spread. He helped fence it himself, and he works with the horses and handles the veterinary chores. Horses have always been part of his life.)

Brewster says he no longer has ambitions to run for major political office, though some day "it may cross my mind," he admitted with a reflective, gentle smile, to come back to the Maryland legislature as a farmer, to work on the things that concern farmers.

Of course he still keeps in touch, is consulted informally by ex-colleagues, maintains political contact of a sort through the alcoholism commission, to which he was appointed two years ago by Gov. Mandel.

Does he miss the Senate?

"No. No more than I miss the Marines. I think about it sometimes, I remember it all right. But I don't miss it. Life goes on. As a young man I was forever thinking of tomorrow. Then with my defeat and illness I thought only of the past. Idealism turned into ambition which turned into alcoholism."

He blames alcohol, by the way, for his drift into a situation that led to his indictment in 1969 on charges of taking a bribe from a mail-order house-Spiegel Inc., for a vote on postal-rate legislation. Six years later, the original charge reduced to accepting an illegal gratuity of $4,5000, Brewster pleaded no contest and was fined $10,000. From the beginning he had denied ever taking a bribe; his lawyers contended that one of his own aides had fabricated the charges.

Today, Den Brewster lives in the present.

"Each day is a new adventure," he said. "I like simple things, and now I have time of 'em: riding - I ride every day, it's my main exercise - and jogging and tennis, the garden, working at the stables. In the old days my appointments secretary ran my life. Now I do stuff that wouldn't even have made her list."

Last week he helped Judy can beans can tomatoes. Twice a week they go to cattle auctions (he has 70 head), and every now and then they slip away to the track to watch their 2-year-old, Early Double, race.

Two and a half days a week he counsels and lectures on alcoholism at a nearby veterans' hospital, helps with its detoxification program, leads group therapy, runs an informal legal clinic. The job pays $100 a week.

He also heads the Governor's Advisory Council on Alocholism - "I see it as part of my recovery" - and works with a quarter-way house in Baltimore. At St. John's Episcopal Church, where he is a vestryman, he serves on a committee dealing with alcoholism.

He is proud of his trim shape. This spring he dieted down to 185 pounds, which looks just fine on his large boned, 6-3 frame, and he came in third in the rugged My Lady's Manor point-to-point steeplechase. He had won that race 30 years ago.

"I tell you, it felt great. Racing at 55 against 20-year-olds."

He is discovering the joys of being old-shoe. He sold the other farm where he held the big political clambakes, impersonal as a PR-man's smile, and in fact no liquor at all is served at his place in the white-fence countryside west of Baltimore.

There are always children around: his own younger son Gerry, 21, and Judy's two, Krista and Kurt Aarsand, 17 and 15, and their friends, and of course the baby, who goes everywhere with them and who now cruised imperturbably through the house and across the lawns, tasting things.

It was time to move to the covered porch. Unceremoniously, Brewster dipped a pail of water from the pool and washed his hands. A crack of thunder made everyone jump, and the big concern was getting Rabbit into the house because she is terrified of thunder and has been known to jump through screen doors in panic. After the fried chicken and beans and corn there would be home-made chocolate-chip ice cream.

He watched the first big drops splatter on the flagstones. "I'm a happy man," he said.