George Bamberger, who turned out a host of 20-game winners as pitching coach of the Baltimore Orioles for a decade and later managed the Milwaukee Brewers and the Mets, died Sunday at his home in North Redington Beach, Fla. He was 80.

He had been treated for cancer, but the cause of death was not known, his daughter Lori Bailey said.

Bamberger, a native of Staten Island, pitched for 18 seasons, but spent virtually all that time in the minor leagues. He had stints with the New York Giants in 1951 and 1952 and the Orioles in 1959, appearing in 10 games with no won-lost record.

He flourished, however, as pitching coach of the Orioles from 1968 to 1977, his pitchers winning at least 20 games in a season 18 times. Jim Palmer won the American League Cy Young award three times under Bamberger and Mike Cuellar was a co-winner in 1969. Palmer, Cuellar, Pat Dobson and Dave McNally were each 20-game winners for Bamberger in 1971, when the Orioles won a third straight pennant.

''He was the best pitching coach I ever saw,'' Frank Cashen, the former general manager of the Orioles and the Mets, said in a telephone interview yesterday.

He recalled that Bamberger gave his pitchers plenty of work.

''He believed in a four-man rotation,'' Cashen said. ''His theory was, the arm was a muscle, and the more you used it, the better off you were, as long as you didn't abuse it.''

Cashen remembered that Orioles Manager Earl Weaver ''was very flamboyant and not afraid to take pitchers to task vocally,'' but that ''George was very quiet; he was their friend.''

In 1979, Bamberger told Dave Anderson of The New York Times: ''My whole idea is to throw the ball over the plate. The most important pitch is a strike. But the trick is to change speeds. Trying to pinpoint a pitch is crazy. Throw the ball down the middle, but don't throw the same pitch twice. Change the speed.''

Taking over a losing franchise, Bamberger managed the Brewers to 93 victories and a third-place finish in the American League East in 1978 and was named the major leagues' Manager of the Year by The Sporting News. He managed the Brewers to 95 victories and second place in 1979, then had a heart attack during spring training 1980. He had bypass surgery and returned in early June but resigned in September.

Cashen, having become the Mets' general manager, hired Bamberger as the manager of a floundering team in 1982. Dave Kingman and George Foster supplied some power, but the pitching was thin, despite the return of Tom Seaver in 1983. Bamberger managed the Mets to a last-place finish in 1982, then resigned on June 3, 1983, with the team en route to last place once more, saying, ''I probably suffered enough.''

He managed the Brewers again in 1985 and 1986, finishing last both times.

In addition to his daughter Lori Bailey, Bamberger is survived by his wife, Wilma; his daughters Judy Sutton and Nancy Baldwin; his brother, Charles; five grandchildren; and three great-grandchildren.