Northwestern's first victory in 35 games overshadowed a more significant milestone in college football Saturday: Coach Eddie Robinson's 300th victory at Grambling State University.

Grambling's 43-21 defeat of Florida A&M at Tallahassee, Fla., made Robinson the fourth coach in history to win 300 games, joining Alabama's Bear Bryant and the late Amos Alonzo Stagg and Pop Warner. Robinson, 63, has won 18 fewer than record-holder Bryant, 69.

Robinson said he "was even higher on cloud nine" yesterday after receiving a congratulatory phone call from President Reagan. "You just don't get calls like that every day."

Robinson graduated from Leland in 1941 and has a 300-98-13 record in his 40 seasons at the small black school in Grambling, La. He has coached several players who became standouts in the National Football League, but one of his best is the player who led the Tigers to victory Saturday night. Swift receiver Trumaine Johnson caught two touchdown passes and returned a punt 64 yards for another score to help Grambling erase a 21-14 deficit.

Howard played well for 25 minutes in a 50-0 loss to Mid-Eastern Athletic Conference opponent South Carolina State before falling apart.

Coach Floyd Keith said he "may consider some offensive changes" after only seven of 27 passes were completed and two of five fumbles were lost.

One of Keith's changes might be replacing Brian Sloan, who completed only five of 20 passes in Orangeburg, S.C. Sloan replaced Sandy Nichols, who is still out with a bruised shoulder.

Navy Coach Gary Tranquill, too, is considering several changes after reviewing film of a 31-0 loss to visiting Boston College. "Other than one (running back Napoleon McCallum) who is only getting better, our skilled position players just aren't getting it done," Tranquill said."They have been very inconsistent. The longer that continues, the more momentum you lose."

Tranquill didn't announce any immediate changes yesterday, but said, "Some (changes) could certainly develop during the week, depending on practice."

At Maryland, Coach Bobby Ross was exceptionally pleased with his team's defensive effort in a 23-6 victory over North Carolina State. Although Ross declined to say whose play most impressed him, defensive guard Mike Corvino and end Howard Eubanks seemed to be in State's offensive backfield more than anyone else.

Maryland's schedule was ranked as the sixth-toughest in the nation going into the season. Now, consecutive games, beginning Oct. 30, against North Carolina, Miami and Clemson are less intimidating.

North Carolina has played two games without tailback Kelvin Bryant, slow recovering from an ankle injury, and probably will play the next three or four without quarterback Rod Elkins, who has had torn cartilage surgically removed from his left knee, injured in the 62-8 defeat of Army.

Miami had trouble defeating Michigan State, 25-22, without quarterback Jim Kelly, who separated his right shoulder in the previous game and is out for the season. Clemson, the defending national champion, has missed its graduated seniors more than expected, winning its first game by beating Western Carolina, 21-10.

Undefeated Duke is first in the Atlantic Coast Conference after beating Virginia, 51-17. Coach George Welsh said his Cavaliers have regressed the last three weeks.