Working at a painfully deliberate pace, Jake Brestowski stuck one missile after another in all the right spots to win the United States Open Darts championship yesterday at the Twin Bridges Marriott.

Brestowski, from Hazleton, Pa., defeated 1975 champion Conrad Daniels in three legs to win the title before 800 spectators in his first U.S. Open competition. Brestowski walked off with $3,700 and a trip to the world title games in England this June.

"I can handle some pressure with no problem," said the exuberant left-hander who was an underdog against the firmly established Daniels. "I've been practicing a lot and I felt pretty good coming into the whole thing."

A paper company employe, Brestowski is looking eagerly toward his trip abroad: "I'm going to work real hard and... I'll handle the pressure over there also."

Brestowski reached the final by beating Rich Kozlusky in two closely contested legs while Daniels was defeating ray Fischer with speedy dispatch. Throughout the early rounds, Daniels became a consensus favorite off the relative ease in which he cruised through his matches.

Daniels, of Hamilton Square, N.J., thoroughly emotionless throughout the finals and semifinals, and was smiliarly stolid after the champion-ship match, accepting his loss with a mildly disappointed shrug. Daniels collected $1,000 in prize money.

The women's title was retained by defending champion Kathi Corcoran of West Babylon, N.Y., in an intense three-leg match with Helen Scheer-baum. Each player had several chances to win with a well placed throw but Corcoran finally prevailed in an unusually time-consuming match.

"I was pretty confident even when the game was so close -- I knew I'd win it," said Corcoran. "Helen just gets too nervous. Her hand was shaking on every throw. I've played Helen before in other tournaments and she's never beaten me. She always seems to get too nervous and it hurts her game."

Corcoran defeated Kathy Fishetti in the semifinals on her way to taking home $350. Despite Corcoran's back-to-back titles, 16-year-old Kathy Karpowich was named the American Darting Organization "darter of the year." Karpowich, of Freeland, Pa., won six titles on the ADO circuit over the last year but was upset in the first round of play Saturday by Mary Healy of St. Louis.

The 1978 men's champion, John Zimnawoda, also was upset in the early rounds Saturday.

In the two-man final, Daniels was back on center stage with partner Ernie Rill of Trenton, N.J., but they were defeated by Bill Glover of Dallas and Dan Pucillo of Los Angeles.

Daniels and Rill had made it to the finals by defeating one of the favored twosomes, Zimnawoda and Rich Brighner. Pucillo and Glover defeated Cam Melchiorre and Drex LeVan in the semifinals.