Once again, Mary Decker Slaney is being asked to take her disappointment lying down.

Only with crutches is Slaney able to get up and around her home in Eugene, Ore. Recent surgery on her right Achilles' tendon has knocked her out of the world track and field championships in Rome, Aug. 29-Sept. 6.

That may seem like merely another setback in the injury-plagued career of America's greatest female distance runner. But missing the world championships is much more significant.

Because of three straight Olympic boycotts, the inaugural world championships in 1983 have been the only meeting of nearly all the world's top track and field athletes since the 1972 Olympics.

That meet also established Slaney as an international runner of the very highest rank. When she beat Soviet competitors to win the 1,500 and 3,000 meters in 1983, she was no longer just a fast runner who made a career of beating Americans and the clock.

Slaney, who holds every U.S. record from 800 to 10,000 meters, hoped to double in the 800 and 1,500 this year. Even the day before her latest surgery, she thought she would at least be able to defend her title in the 1,500.

It wasn't the operation alone but what the surgeons found that has knocked Slaney off the track until at least July, probably for much longer. "She had more wrong than we thought," said her coach, Luis de Oliveira. "We thought it would just be minor."

He said Slaney now understands that missing the world championships is a foregone conclusion.

To compete in Rome, she would need to qualify as one of the top three finishers at the USA/Mobil national championships June 25-28. Because Slaney has not run in a major race in 20 months, she has not met the entry standards for the nationals.

Slaney's agent, Brad Hunt of Advantage International, said he saw a way Slaney could be added to the U.S. team for the world meet.

He outlined a scenario that began with some of the top finishers in the national meet not meeting qualifying standards for the world meet, in which each country can have up to three runners per event. Slaney would then (1) have to run a qualifying race before Aug. 16 and (2) have to get a special dispensation from The Athletics Congress, which governs U.S. track. Neither is likely.

Dr. Stan James, the physician who operated on Slaney, said, "Our goal now is next year."

Slaney, 28, had planned 1987 as a comeback year following the birth of her daughter and the surgery last November to clean out old scar tissue in her Achilles' tendon. The plans began to unravel when sharp pain in the Achilles' area resulted in a last-minute withdrawal from the mile at the May 15 Pepsi Meet in Los Angeles.

That decision was based on sacrificing one race to save the season, and it showed sensible restraint for a woman who has always run headlong into problems. But it didn't substantially help her foot, and she needed surgery on the tendon for the third time since 1981.

"Mary is very disappointed because the world championships were very important to her," Hunt said. "She has had setbacks, emotionally and physically, in the past, and she is prepared to deal with this one."