The Navy's handling of the investigation into the USS Iowa explosion has exacerbated concerns in the Pentagon and Congress about the credibility of the U.S. military as it enters a critical period of redefinition and restructuring, according to a number of officials.

The Iowa episode is the latest in a series of high-profile blunders, mishaps and misleading pronouncements in recent months. While they do not bear directly on the defense budget, they have helped erode public confidence in the armed forces' leadership, and may further complicate the military's ability to present its case in budget battles later this year.

Last week, the Navy was forced to back off its conclusion that the battleship Iowa explosion, in which 47 sailors were killed, was "intentional" sabotage "most probably" committed by a suicidal crew member. Further investigation, ordered by Congress, found major flaws in the Navy technical inquiry and outlined other probable causes, including a simple accident, based on studies by scientists from Sandia National Laboratories.

The bungled Iowa investigation has fueled existing complaints by congressional budget-cutters that the services have stubbornly resisted calls to seriously reexamine their traditional roles and missions in a new era of East-West relations.

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, said top Navy officials had been "unhelpful in the extreme" in presenting new ideas about how to shrink the Navy and cut operating costs.

Where the Army has heralded a plan to cut personnel by one in four over the next five years, a former Army chief of staff said two in four would be more appropriate.

Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, called recently for a top-to-bottom reexamination in the military. But days later the services offered five-year plans that failed to deal with the toughest questions about how to eliminate duplication, redundancy and the expensive wartime operating tempo the services are seeking for the future.

Military leaders concerned about the credibility issue are for the most part loath to discuss it, but warnings from the upper reaches of the military establishment abound.

Powell reminded the troops recently that the public has little inherent trust of the military and rough waters may be ahead. "We swear to defend a Constitution that would like us to go away -- a document that looks at the military, and in particular . . . the Army, as an unfortunately necessary institution, useful in times of crisis, but to be watched carefully at all other times," Powell wrote in the May issue of the Naval Institute's magazine.

New findings that the Iowa explosion could have been triggered by a simple accident followed a Navy investigation that spent millions of dollars on what Navy officials asserted was a thorough and unassailable technical inquiry.

Frank C. Conahan, assistant comptroller general, told the Senate Armed Services Committee, "A close evaluation of the way the Navy went about doing their investigation would come to a conclusion that perhaps too early on in the investigation they ruled out other possible or plausible causes for the explosion."

But the other services have suffered similiar embarrassing reversals.

The Air Force, which employed for the first time its F-117A "stealth" fighters in the Panama invasion last December, was forced to reverse its public assertion that the planes had carried out their mission with flawless precision.

Confronted with photographs showing one of the 2,000-pound bombs had missed its target by a wide margin, the Air Force acknowledged to Defense Secretary Richard B. Cheney that it had provided him with incorrect information.

The Panama invasion also seriously strained the Army's credibility. Army units improperly violated a diplomatic residence, blared loud rock music at the Papal Mission where Gen. Manuel Antonio Noriega had taken refuge and made inflated claims of cocaine stashes found in Noriega's headquarters. In one instance, the substance Army officials claimed was cocaine turned out to be tamale paste wrapped in banana leaves.

After the invasion, Lt. Gen. Carl W. Stiner, the airborne commander, alleged that the timing of the invasion had been "compromised," or deliberately leaked, and that as a result the first paratrooper to jump over Rio Hato was shot dead by waiting Panamanian forces. Many of Stiner's statements about the alleged "compromise" later were retracted as wrong by the Pentagon and, according to Army officials, the first paratrooper at Rio Hato "is alive today," having recovered from a neck wound.

Sen. William S. Cohen (R-Maine) recently questioned Stiner in private on whether the Army had followed standard procedures during preparations for the Panama invasion by seeking authorization to conduct certain covert reconnaissance and other preparatory operations on the ground.

Cohen reportedly was surprised when Stiner replied that he had bypassed the requirements in the interest of time.