BARCELONA ’92 OLYMPICS / DAY 6 : Karnaugh Must Get Past Grief : Swimming: U.S. athlete, whose father died at opening ceremony, competes today in 200 individual medley.

BARCELONA — The longest, most punishing week of Ron Karnaugh’s young life comes to an end on the world stage today when he swims in the Olympic 200-meter individual medley. The race is being contested six days after Karnaugh’s 60-year-old father, Peter, died of a heart attack during the opening ceremony.

Karnaugh, 26, from Maplewood, N.J., will swim first in a morning qualifying heat and then, if he makes it, will swim tonight in the final, on the last night of theswimming competition.

Under ordinary circumstances, Karnaugh would be considered a probable medalist. His time of 2:01.56 ranks second in the world behind defending Olympic champion and world record-holder Tamas Darnyi of Hungary. Karnaugh, who has competed with the Mission Viejo Nadadores since his graduation from Cal two years ago, won the U.S. trials last March.

Karnaugh, however, has been under extraordinary stress this week. He arrived with the U.S. team at the Olympic village 10 days ago and was one of the few U.S. swimmers to march in the opening ceremony last Sunday night. Less than an hour after Karnaugh had spotted his father, mother and sister in the stands, his father collapsed. He died shortly thereafter at a first-aid clinic at Olympic the stadium.

Two other factors:

--Most of the U.S. rankings have proved somewhat artificial, because the U.S. trials were exceptionally competitive and fast. Swimmers from other countries have, in many cases, had to peak only for the Games and have swum faster than their rankings. So Karnaugh is clearly in a difficult race.

--There will be intense scrutiny on Karnaugh and extremely heavy media coverage of a race that otherwise would have been largely ignored.

To that end, Karnaugh’s mother and sister have tried to shield him from the details of returning the family--and his father’s body--to the United States.

“His mother has really tried to prevent Ron from dealing with any of this and just to concentrate on swimming his race,” said a friend who has been working with the Karnaugh family. “It really has been the most important thing for them.”

Still, after first announcing that he would swim in spite of his father’s death, Karnaugh told teammates as recently as Tuesday that he didn’t know how he could possibly concentrate on swimming.

Teammates said that attitude has changed in the last two days and that Karnaugh now expects to swim well. They have been told, however, not to give interviews regarding Karnaugh.

He has been working out each day with his coach, Terry Stoddard, who earlier this week called the workouts “business as usual.”

On Thursday, George Steinbrenner, who has attended each night of the swimming competition, said that he had arranged to pay Karnaugh’s tuition at the University of Medicine and Dentistry of New Jersey in Newark.