George Bush, hoping for new campaign life, trounced Republican Party presidential front-runner Ronald Reagan at the Maine state GOP convention yesterday. Reagan returned the compliment, stampeding Bush in Nevada.

President Carter, meanwhile, maintained his popularity among Democrats in Iowa, Oklahoma and Virginia and picked up an additional convention delegate in Mississippi.

Looking for momentum going into his crucial head-to-head faceoff against Reagan in Tuesday's Pennsylvania primary, Bush claimed 17 of Maine's 21 national convention delegates.

But in the weekend round of political oneupmanship, Reagan shut out Bush at the Nevada state GOP convention in Reno, winning the entire slate of 17 national nominating convention delegates.

The former California governor also opened up a wide lead over Bush in the competition for Minnsota's 34 delegates to the national convention. With the GOP holding conventions in two of the state's congressional districts, Reagan blanked Bush 6-to-0. The remaining 28 delegates will be selected at subsequent conventions.

On the Democratic side, Carter faced a new test of his popularity in Iowa, nearly three months after he opened his reelection campaign with a convincing 2-to-1 victory over Sen. Edward M. Kennedy in local caucuses.

With three of Iowa's six congressional district conventions reporting, Carter had 10 delegates to Kennedy's five, and one uncommitted.

Carter trounced Kennedy as Oklahoma Democrats held conventions in each of the state's six congressional districts. The initial results showed Carter sweeping the 1st District in Tulsa, where much of Kennedy's strength in the state was concentrated.

The Oklahoma conventions were to select 29 of the state's 42 national convention delegates. Carter came away with 24 of the delegates, while only three went to Kennedy, and two were uncommitted.

The president blanked Kennedy in Mississippi, where Democrats selected the state's 32 national convention delegates.

During a campaign stop in Wilkes Barre, Pa., last week, Edward M. Kennedy took time out to call Mrs. Gwendolyn Kopechne, the mother of Mary Jo Kopechne, the young woman who died in the Chappaquidick incident. The senator thanked Mrs. Copechne for her comments in support of his candidacy in a recent newspaper interview. He said she closed their brief conversation by assuring him she would vote for him in Tuesday's presidential primary.