A fiercely competitive United States Army lieutenant named George Patton placed fifth in the inaugural Olympic modern pentathlon at Stockholm in 1912.

Since then, the time and effort expended by U.S. competitors has not been matched by results, as Americans have won but tow individual silvers and two bronzes, plus two silvers and a bronze in the team category.

Nevertheless, the search for gold continues unabated at Fort Sam Houston, Tex., where the U.S. team is headquartered and where, each year, 40 boys and 40 girls are chosen to attend an Olympic development clinic.

Eventually, it is hoped one of these youngsters will capture an elusive gold in this gruelling five-days test involving riding, fencing, shooting, swimming and cross-country running.

Sweden, Hungary and the Soviet Union have been the big winners in previous years, although Great Britain surprised by making its first Olympic medal the team gold at Montreal. The British path to victory was smoothed by the ouster of the Soviet team, after Borts Onischenko was caught with a rigged epee during the fencing competition.

The Americans missed the bronze by only 110 points following a disappointing seventh-place finish in the concluding run.

"If we had shot halfway decent, we (still) would have placed," said Col. Jim Moore, officer in charge of the modern pentathlon facility. "We're working very hard on that and on the fencing. Each day we will practice three or four sports, but those two need the most work."

Many Americans who attempt the modern pentathlon are accomplished swimmers and a 1976 Olympian, Robert Nieman, set a world record of 3:13.6 for 300 meters although he finished 26th overall.

The modern pentathlon team lures potential stars through advertise ments in Swimming World and Runners World magazines, through information dispensed by the National Rifle Association and through sports clinics conducted in military recruiting commands.

Training is conducted at Fort Sam Houston and junior and senior teams are selected for overseas competition. As yet, there is no Olympic competition for women, but a world championship was inaugurated in 1977 and when women are added to the Olympic program, the U.S. hopes to be ready.

The national championship will be conducted at Fort Sam Houston July 3-11, with four-man teams - of which three compete - chosen for the men's world senior competition at Budapest Aug. 12-16, the men's junior title meet at The Hague Sept. 21-30 and the womenhs World Cup at Warsaw Aug. 26-29 and Sept. 3-6.

Off his sixth-place finish in the Montreal Olympics, the brightest U.S. hope for Moscow is John Fitzgerald, an Army reservist who excels at shooting and fencing, the events that usually doom American medal hopes.