More than 150 youthful gymnasts from the eastern United States and Canada will participate in the annual Capital Cup gymnastics competition, the Washington area's largest invitational gymnastics meet, Saturday and Sunday at Montgomery College in Rockville.

Hosted by Marvateens Gymnastics of Rockville, the meet will draw such leading gymnastics clubs as the Parkettes of Allentown, Pa., winners of last year's meet; the Cambridge Kips from Canada; Niagara Frontier from New York; Omni from northern New Jersey, and Muriel Grossfeld's from New Haven, Conn.

Among the leading gymnasts are expected to be Mary Lou Retton of the Aerial Port Gymnastics club of West Virginia, Stacy Gusky of Miami, Nancy MacDonald of the Starlettes gymnastics club of New Jersey, Dawn Maurelli of Marvateens and Cheryl Weatherstone, a member of the British national gymnastics team, who is training with Berks Gymnastics Club in Reading, Pa.

Lisa McVay of La Plata, Md., a Marvateens gymnast who finished ninth in the Junior International Invitational last summer in Tokyo, will compete only in the balance beam exercises. Cheryl Kaneshiro, 12, of Rockville, who recently won a spot on the United States Gymnastics Federation Junior Competitive Team, will perform on the uneven bars and the balance beam.

Preliminary competition is scheduled for 9 a.m., 1 p.m. and 5 p.m. on Saturday. On Sunday at 2:30 p.m. the top 10 finishers for each of the individual events, uneven bars, balance beam, floor exercise and vault, will meet in the final round.

Tickets for Saturday's events are $4 for adults and $3 for children under 12. All tickets for the finals are $5.