WASHINGTON — After a string of deadly accidents in the western Pacific, a top admiral acknowledged on Thursday that the Navy had knowingly operated warships there despite a growing number of major training and maintenance shortfalls — all to meet increasing operational demands.

An unusual hearing of two House Armed Services subcommittees offered no new information about what caused four Navy mishaps in the western Pacific this year, including two fatal collisions between Navy destroyers and foreign cargo ships that left 17 sailors dead. Those accidents remain under investigation.

But the hearing painted a disturbing portrait of fatigued crews and commanders on a shrinking overseas fleet saddled with constant deployments — including confronting an expansionist Chinese military and keeping vigil on a nuclear saber-rattling North Korea — with little time left to train or to repair aging ships.

“The Navy is caught between unrelenting demands and a shortage of ships,” John H. Pendleton, a director of the Government Accountability Office, the investigative arm of Congress, told lawmakers. The office has chronicled the Navy’s woes in several recent reports.