Four years after the Navy discovered that it had purchased defective fire hose nozzles from a disreputable firm, 52 of the nozzles still were in use last month aboard aircraft carriers, destroyers and other combat vessels, a Navy official testified yesterday.

None of the defective nozzles was aboard the USS Stark when it was struck by Exocet missiles in the Persian Gulf May 17, setting off a fire that killed 37 sailors. But Rear Adm. Robert B. Abele told a Senate subcommittee that the Navy's failure to recall the faulty nozzles may have endangered lives of thousands of other Navy personnel.

"It could have posed the potential of impeding a ship's ability to fight a fire," Abele told the Governmental Operations permanent subcommittee on investigations. " . . . This obviously was a big hole in the {safety} system."

Abele, vice commander of the Naval Supply Systems Command, testified during the first of two days of scheduled hearings on military procurement fraud and the Defense Department's efforts to combat it.

Sen. William V. Roth Jr. (Del.), ranking Republican on the panel, and other members said the military may not be aggressive enough in prosecuting, suing or debarring fraudulent contractors, nor has it done enough to track down defective equipment once it enters the system.

Roth said those faulty parts are "ticking bombs waiting to explode before U.S. military personnel."

Subcommittee Chairman Sam Nunn (D-Ga.) said it is "outrageous" that military personnel are being asked "to risk their lives at the hands of their own equipment."

"We need more effective ways to protect our armed forces from these potential consequences," Nunn said.

The hearings touched on a wide range of fraudulent contracting practices, including a case in which a California aerospace subcontractor, The Spring Works, sold substandard springs for use in aircraft braking systems, landing gear, wing flaps and cabin pressure valves.

Between 1978 and 1985, those springs were used in the space shuttles Atlantis and Discovery; F14, F15 and F18 jet fighters; B1 and B52 bombers, and the MX, Minuteman, Pershing, Titan II and cruise missles, according to Stephen H. Levin, staff counsel to the subcommittee.

Derek J. Vander Schaaf, the department's deputy inspector general, said his office has been especially aggressive in going after procurement fraud, but there are limits to what the government can do to monitor the quality of materials purchased.

"Our system is very, very dependent upon the honesty and integrity of the contractor out there," he said.

The faulty nozzle problem was uncovered last month by subcommittee staff members while they inspected firefighting equipment aboard the USS Nassau, an amphibious assault ship at Norfolk Naval Station. A later investigation determined that 375 of the faulty nozzles still were in circulation, 52 of them aboard naval vessels and the remainder stored at various installation.

The Navy purchased nearly 3,500 nozzles from Alchemy Inc., a Pennsylvania firm, in 1981 and 1982. Defects in the nozzles, resulting from use of inferior materials, were discovered during a firefighting drill aboard the USS Fulton in 1982. The following February, the Fleet Material Support Office sent a message to fleet commanders ordering that they confiscate and dispose of the faulty nozzles.

Abele said yesterday that the Navy assumed all commands had carried out instructions. "In hindsight," he said, "that was an erroneous assumption."