RAPID CITY, S.D. (AP) _ The second crash of a B-1B bomber in nine days probably will not force another grounding of the nation's fleet of advanced jet bombers, an Air Force general said Friday.

The four crewmen parachuted to safety Thursday night, but the $280 million plane was destroyed after smashing onto a runway at Ellsworth Air Force Base during a routine training flight.

The crash came two days after officials reported that the Air Force had inspected and cleared more than two-thirds of the 98 B-1B bombers, which were grounded briefly following a crash Nov. 8 that destroyed a plane in Texas.

The plane involved in Thursday's crash underwent a three-hour inspection Monday and was cleared for flight, Air Force officials said.

''I see no reason to believe we will ground the fleet. I've talked to my bosses, and there is no intention at this time to ground them,'' said Brig. Gen. Robert Marquette Jr., commander of the 12th Air Division at Ellsworth.

The Ellsworth crash and a B-1B crash last week in Texas do not appear to be linked to the same cause, Marquette said after a tour of the crash site. ''We have evidence there was an engine fire'' in the Texas crash, he said.

It will take a team of military and civilian experts at least 30 days to evaluate crash evidence, he said.

The ejection system can propel crew members 100 to 150 feet into the air, allowing them to parachute safely to the ground, he said. Marquette said he did not know how fast or high the plane was flying when the crew bailed out.

Marquette refused to speculate on the cause of Thursday's crash but said there was no evidece of an engine fire. At least one witness reported seeing an engine on fire before the crash.

An Air Force statement released at the Pentagon in Washington said there was no fire on board, and Pentagon sources said Thursday the plane apparently clipped utility lines as it came in for its final landing.

The long-range strategic bomber was trying to land when it crashed at 10:40 p.m., toppling a utility pole that cut off power to two schools and a housing area.

''I could hear the plane coming in for a landing,'' said John Hanzel, who lives next to the base. ''I heard a muffled boom. It just lit the field up, probably for about 10 minutes.''

''The engine was on fire before it (the plane) hit the ground,'' witness Dale Landreth told Rapid City radio station KOTA.

Another eyewitness, Ron Fisher, said, ''We saw a big ball of fire that lit up the sky.''

Todd Heinle, a police officer in the nearby town of Box Elder, said he was less than a mile away in a convenience store parking lot and noticed the plane because of a noise.

''It almost sounded like the plane was trying to increase in power. It was making a weird noise,'' Heinle said.

He and a fellow officer saw the wings tilt one way and then the other way, then the lights in the plane went out. ''It was just a split second after the lights went out, there was an explosion and the flames started to come up.''

Heinle drove to an area close to the wreckage near the runway and saw the plane on the ground. ''The plane was laying on the ground in flames,'' he said. ''It was pretty much destroyed.''

One of the four crewmen was injured, said Sgt. Tony Evans of the Ellsworth public information office. The crew members were identified as: Capt. Mick R. Guthals, pilot, Los Alamos, N.M.; Capt. Grover M. Gossett, offensive systems officer, Aiken, S.C.; Major Dean C. Spraggins, defensive systems officer, Voorheesville, N.Y., and Major Thomas C. Skillman, aircraft commander, Bellmeade, N.J. Spraggins, the injured crewman, was listed in good condition at Lackland Air Force Base in Texas for treatment of a back injury.

The crash was the fourth in the four years since the United States began flying B-1 aircraft, the nation's first new long-range bomber in more than 25 years.

Last week, a B-1B crashed in a field near Dyess Air Force Base in west Texas. The crew of four ejected and survived.

The long-range bomber built by Rockwell International is designed to fly at high speed and low altitude and deliver nuclear weapons.

Marquette said he couldn't comment on whether the plane carried nuclear weapons.But the Air Force statement Thursday said: ''The bomber carried no weapons. There was no fire on board prior to the crash.''