At the age of 71, Gardnar Mulloy won his 72nd and 73rd national tennis titles yesterday at Army Navy Country Club in Arlington.

In a rematch of last year's final, Mulloy defeated Fritz Klein of Gladwyne, Pa., 7-5, 6-3, to win his second consecutive 70-and-over National Clay Court singles title.

In the doubles, the side of the sport in which Mulloy achieved his greatest reknown when he won four U.S. championships with Billy Talbert in the 1940s, Mulloy and Verne Hughes of Laguna Hills, Calif., defended their title by beating Charlie Swanson of Narragansett, R.I., and Harry Hoffman of Elkins Park, Pa., 6-3, 6-3.

When Klein, a retired engineer who won the 70-and-over singles world championships earlier this year in Australia, took a 4-0 lead in the first set, it appeared Mulloy might have difficulty defending his clay court title.

Mulloy won his first game when he broke Klein in the fifth game. "I figured I had a chance," Mulloy said. "I'm only down one service break. If I hold my serve and break him again, I'm okay."

Mulloy did just that. He tied the score, 4-4, with a drop shot and went ahead, 5-4, when Klein hit a cross-court backhand and Mulloy dropped a winner into the open court.

But Klein broke Mulloy for the third time in the 10th game. "Clay is slow to begin with and these courts were soaked, so the serve wasn't much of a weapon," Mulloy said.

Mulloy broke Klein again, the seventh service break of the set, to take a 6-5 advantage. He won the set when Klein hit a lob long.

In the second set, Mulloy, up two breaks to one, held a 3-1 lead. Klein broke Mulloy to tie the score at 3. Mulloy broke Klein in the seventh and ninth games, winning the match with a lob after he had brought Klein to the net with a drop shot.

Mulloy didn't think playing singles and doubles was especially noteworthy. "You got to do, what you got to do," he said.