U.S. military officers are resisting congressional calls for a 30-day suspension of training flights using night-vision goggles, asserting the flights are getting safer and are essential to a round-the-clock fighting capability.

But members of the House Armed Services investigations subcommittee say they need to be convinced that the use of night-vision goggles has not been a factor in a rash of recent deadly crashes.The debate over the goggles was aired Tuesday in a hearing of the subcommittee in the immediate aftermath of a helicopter crash Monday during training exercises in South Korea. Nineteen Marines were killed and 16 were injured in the second Marine helicopter disaster in South Korea in four days.

Rep. Nicholas Mavroules, D-Mass., the subcommittee chairman, said 43 servicemen were killed over the last year in four separate helicopter crashes during flights in which night-vision goggles were used.

He said an inquiry by the panel determined that over the past two years, 27 of the most serious accidents, or more than 50 percent of the total, involved the use of night-vision goggles.

"This steep upward trend is very, very alarming," Mavroules said.

He and other subcommittee members said they doubt the safety of an early version of the night-vision goggles and are disturbed that many of them are still in use. The chairman also questioned whether the initial flight training using the goggles is sufficient and whether one hour every 45 days is enough follow-up training.

"The restricted field of vision, limited depth perception, inability to see certain obstacles and many other factors adversely impact upon the aviator's ability to fly the aircraft," Mavroules said.

One witness, veteran Army flight instructor David E. Broadnax, urged suspending night training using the goggles for 30 days and added, "I feel we should slow down for a moment at least, pull over to the side of the road and take a critical look at what we're doing."