ANNAPOLIS, Md., April 29--The Harvard lightweight crews completed their third sweep of the season against Navy and Georgetown on the Severn River here today.

The Crimson varsity moved out to a three-seat lead after the first 30 strokes. As the stroke settled from a 41 to a 37, and ten strokes later to a 33, Harvard pulled away another length-and-a-half.

With captain Gibby Vincent settled in the number three seat and new addition Chris Cutler in his varsity debut at two, the varsity sprinted home at 37 into a rising headwind. The 6:37 time marked a three-length margin over the Midshipmen.

Plebes Lose

The first freshmen started the afternoon with a 2 1/2-length victory over the Plebes, with Georgetown a distant third all day, even farther back. The J.V. fell three seats behind on the start, but built a 2 1/2-length lead in the body of the race with strong, steady rowing.

Next weekend the lightweights travel to New Haven to face Yale and a highly regarded Princeton eight in the final tune up for Cornell and Penn at the Sprints.