It has often cost a lot less to cremate than to embalm and ensepulcher a corpse, but an alert astronaut and his buddies may change all that with their project to rocket the ashes into outer space for roughly $4,000.

The Celestis company of Melbourne, Fla., has contracted with Space Services Inc. of Houston to build the launch rockets. Former astronaut Donald (Deke) Slayton heads the firing end of the business. Slayton has said little capsules containing the ashes would wind up in the Van Allen radiation belt 1,900 miles distant and would not violate a general agreement to keep space free of orbiting clutter.

You would have the body cremated the usual way, but instead of getting a peck of ashes to toss about the Shalimar Gardens or other lovely spot, you would turn them over to Celestis for a "further reduction," to fit into a capsule two inches long, half an inch wide.

John Cherry, a spokesman for Celestis, told Reuter news service that marketing efforts will begin in 30 days. The company believes there is a substantial public interest in the project and it hopes to attract many customers from England and Japan as well as here.

The capsules will be of titanium, designed by space engineers, Cherry said, and could be engraved with a cross or other religious symbol along with the person's name and Social Security number. It was said the capsules would orbit the earth for 63 million years.

Attempts to reach Cherry in Florida were unavailing yesterday. It is not yet clear whether the Social Security number is for purposes of future taxes or not, and it is not known what happens to the mortal remains after the 63 million years, or what redress the purchaser has if the system should somehow fail after, say, 57 million years.

Slayton, reached in Texas, said it depends on the trajectory how long something stays in orbit, and the trajectory chosen is for 63 million years. It is understood an occasional diehard might object, but Slayton said he believed that for most people 63 million years "would seem long enough." He was not privy, he said, to the "further reduction" process of getting people into the capsules, but foresaw no problem shooting them into the right trajectory once they were there.