Jim Lynam, who led St. Joseph's college into the final eight of the NCAA basketball tournaments this season, was named assistant coach of the Portland Trail Blazers of the National Basketball Association last night. p

Lynam, 39, who coached the Hawks for three seasons after five seasons as coach at American University, accepted the job as Jack Ramsay's top assistant yesterday before leaving for Puerto Rico to coach in a summer league there.

Lynam is a close friend of Ramsay's, having played for him when Ramsay was the coach at St. Joseph's in the early 1960s. He had considered taking a similar position under Ramsay two years ago but decided to remain at St. Joseph's because he had just finished his first year at the Philadelphia school.

Jim Boyle, Lynam's top assistant, is considered the leading candidate to replace Lynam. The press release that St. Joseph's will put out today reportedly mentions that Ramsay recommended Boyle to Athletic Director Don DiJulia as a replacement for Lynam. Boyle, a St. Joseph's assistant the last eight seasons, was a teammate of Lynam's at the school.

Lynam had apparently been considering the move for the last few weeks but did not make a final decision until yesterday.