Laurie Kaiser of St. Paul, Minn., an elfin gymnast with a fetching smile, captured top honors yesterday at the fourth annual Capital Cup Women's gymnastics championships. She won first place in the floor exercise and balance beam and tied for first in the all-around.

Keiser, 15, delighted a full house at Montgomery College in Rockville with a captivating floor routine, set to circus music, that featured a double back flip, a double full twist and a full twist in with a back flip out. She received a 9.6 in the event in the final round of the championships.

Kaiser scored a 9.6 on the balance beam with an intricate, almost flawless routine that included a neatly executed punch front flip with a double back dismount.

"This is the first time I've won so much in a tournament this big," said Kaiser, a veteran of 10 years in gymnastics.

Marcia Frederick, 17, of New Haven, Conn., 1978 world uneven bars champion and a member of the 1980 U.S. Olympics women's gymnastic team, won first place on the uneven bars with scores of 9.7 yesterday and 9.3 Saturday night for a total of 19.

Complaining of sore ankles, Frederick dropped out of the floor and vaulting exercises Saturday night. Her ankles still bothered her yesterday, and it showed when she fell from the balance beam and then stumbled slightly on a double back dismount for a less than Olympian score of 8.4. "I hurt one ankle in China," said Frederick, "and then I over-compensated and hurt the other."

Frederick was magnificent on the uneven bars, however, soaring above the high bar, a move that she developed and is now named after her.

"It was invented by a man in Japan, I don't know his name, for men's gymnastics," said Frederick. "I changed it a little because it is a hard move for women to do."

Maisie Chillano, 15, of Norristown, Pa., won the vaulting exercise with a superbly executed half twist onto the horse and a back somersault off in a layout position.

"I just learned that vault this year. "I've been doing it off and on this fall," said Chillano.

Stacey Kaplan, 14, of Rochester, N.Y., who Saturday night tied Kaiser in the all-around at 36.75, failed to win any firsts in the single event finals yesterday.

The Maryland Marvateens gymnastics club was host for the competition, which attracted more than 300 gymnasts from 43 clubs in 14 states.