VANDENBERG AIR FORCE BASE, Calif. (AP) _ A Titan 2 rocket that once sat in a silo armed with a nuclear warhead was launched into space Monday, carrying a secret Air Force payload believed to be four spy satellites designed to eavesdrop on Soviet ships.

The launch marked the first time one of the refurbished missiles had been used as a space booster, and apparently was the second time U.S. spy satellites had been sent into orbit in less than a week.

''It was a spectacular launch with all systems operating as expected,'' said Air Force Capt. Norma Payne.

But the spokeswoman added that officials would not know for two to three days whether the classified payload achieved its intended polar orbit circling the Earth from North to South poles.

The rocket almost certainly carried a four-satellite addition to the Navy's White Cloud Navy Ocean Surveillance System, an electronic eavesdropping system that locates and identifies Soviet and other ships by detecting radio and radar transmissions, space policy analyst John Pike said before the launch.

''The Navy really likes them,'' said Pike, of the Washington-based Federation of American Scientists. ''They are very important for being able to keep track of the Soviet fleet.''

Pike said a White Cloud launch ''consists of one mother satellite and three subsatellites,'' and that when orbit is reached, the mother satellite deploys the other three spacecraft so all four are strung out a few hundred miles from each other in polar orbit.

The $37.5 million Titan 2 roared off Space Launch Complex 4 West and into fog-shrouded skies at 2:25 a.m. PDT, Ms. Payne said at this sprawling military base 140 miles northwest of Los Angeles.

The force of the blast-off rattled windows in the nearby town of Lompoc, where police said they received a half-dozen calls from residents asking whether it was an earthquake or a launch.

The liquid-fueled, two-stage rocket is 103 feet high and capable of lifting 4,200 pounds into a 100-nautical-mile circular orbit.

Starting in the 1960s, Titan 2 rockets were kept in silos in Arkansas, Kansas and Arizona, where they served as intercontinental ballistic missiles, each carrying a nine-megaton hydrogen warhead.

But the missiles were removed from service ''because the propellants were corroding the innards of the missile and they had a tendency to blow up,'' Pike said.

The Air Force then ordered 13 Titan 2s reconditioned as space boosters under a $528.9 million contract with Martin Marietta Corp. Air Force officials have said more are likely to be refurbished because recycling the old ICBMs is cheaper than building new rockets.

Last Friday, a satellite said to be designed for intercepting Soviet communications was launched by a $65 million Titan 34D rocket from Cape Canaveral, Fla. But a source close to the project, who spoke on condition of anonymity, said the spacecraft failed to achieve its desired stationary orbit 22,300 miles high when the upper stage of the rocket failed to re-ignite. He said there was little hope of salvaging that mission.

Despite that failure, Air Force Secretary Edward C. ''Pete'' Aldridge issued a prepared statement after Monday's launch, declaring, ''This is the year of space launch recovery.''

''Today's successful Titan 2 launch is the first of three new boosters the Air Force will launch in the coming year,'' Aldridge said. ''The Titan 2, Titan 4 and the Delta 2 ... will ensure this nation's access to space for many years to come.''

The launch had been expected a week earlier, but apparently was delayed by a fuel leak that the Air Force said spurred evacuation of the launch pad Aug. 28. No one was hurt in that incident, officials said.

Pike said the only other payload the Titan 2 might boost into orbit from Vandenberg was a Defense Meteorological Support Program satellite. But he called that unlikely.

A Titan 2 exploded in its Arkansas silo on Sept. 19, 1980, killing one crewman, injuring 21 others, blasting a 250-foot-wide crater and lofting the nine-megaton warhead harmlessly 200 feet from the silo. Fuel leaks and vapor spurts that prompted brief silo evacuations also plagued Titan 2 ICBMs, which since have been replaced by Minuteman, Midgetman and MX missiles.

Pike said Air Force officials have testified before Congress that the first 13 reconditioned Titan 2s would be used for one launch of a LANDSAT Earth- observing science satellite, six launches of DMSP weather satellites and six launches of satellites in a classified program.

Four or five sets of White Clouds - about 16 to 20 satellites - already are in orbit, with the new set likely meant to replace aging White Clouds launched in the early 1980s, he said.

Pike compared White Clouds to Soviet RORSATs, or Radar Ocean Reconaissance Satellites, which monitor U.S. ship movements.