Singer John Denver, who has applied to fly in a space shuttle, will have to content himself with only being "Rocky Mountain High" for at least the next 20 years, NASA officials said.

"I think the country made a mistake when we tried to involve people other than those who are specifically trained for scientific work or have a mission job to do. It sent out a signal that (the shuttle) was safe enough for everybody and that's not right," said J.R. Thompson, director of the Marshall Space Flight Center."There's still a lot of risk in the space shuttle and we only have one John Denver. We ought to keep him on the ground for awhile," Thompson said.

Denver and other civilians who want to fly in a shuttle should have their applications delayed 20 years or more, Thompson said.

"This is going to be a high-risk business for some time to come and we ought to limit it to the professionals," he said Tuesday.

"I'd love to ride the shuttle myself, but that's something that's beyond my lifetime."

Denver, whose space flight application has been rejected by the National Aeronautics and Space Administration, is negotiating to ride a Soviet rocket up to their orbiting space station.

But Denver will need more than a guitar and nice voice if he is to achieve his dream of soaring into space aboard a Soviet flight, the Tass news agency reported Thursday.

Tass said Denver will have to pay $10 million, learn Russian, spend a year training in the Soviet Union and become a proficient jet pilot before he is considered a worthy candidate for a Soviet space flight.

Denver, whose ambition is to soar into space either in a U.S. shuttle or on the Soviet space station Mir, asked Soviet officials in 1982 for the chance.

Tass agreed that it is quite possible for Denver to make a flight, so long as he meets the requirements.

"Denver's singing and guitar playing will, of course, brighten up the life of the Soviet space platform's resident crew on an endurance mission but he needs something more to qualify for a stint aloft," Tass said.

"First, he has to pay $10 million, which is the rough cost of a passenger's eight-day stay in orbit on a commercial basis," it said. "The sum can be lowered if the aspirant for the flight suggests an interesting research program - and then carries it out in space."

Then, the agency said, Denver would have to pass a stringent medical examination before being allowed to enter cosmonaut training at Star City outside Moscow.