The space shuttle Enterprise all but completed its eight-month testing program yesterday with what scientists said was a "superb" flight that proved the craft can return from space missions.

Described as the most important flight in the test program that began here last February, the 2 1/2-minute diving glide of the Enterprise was made without the tailcone that had made previous test flights smoother than actual returns from orbit would be.

"It went better than most of us expected," said Donald K. Slayton, manager of the appraoch and landing tests.

"I'm sure there aren't going to be any problems flying it back [from space] now," said the craft's commander, Joe Engle, who flew the Enterprise along with poliot Richard Truly.

The powerless shuttle, released from atop a Boeing 747 carrier plane at an altitude of 20,500 feet, coasted toward the desert floor at a much steeper angle than on three previous flights.

Slayton said that the principal mile-stone now remaining is testing of the engines, now expected to begin in March, 1979. One more landing test remains here. Now scheduled for Oct. 26, it will be essentially the same as yesterday's flight except that the shuttle will land on a 9,000-foot-long concrete runway.

Engle and Truly put the Enterprise down on the lake-bed with a roll of only 5,000 feet.