If war broke out in Europe the United States would run out of replacements before draft registration or even the draft could do any good, according to Gen. Bernard W. Rogers, commander of North Atlantic Treaty Organization forces.

Rogers, supreme allied commander in Europe, made that point emphatically in previously secret testimony released in censored form by the Senate Armed Services Committee this week.

His testimony is one reason why military leaders say that draft registration, though a plus symbolically, will do little toward sustaining the all-volunteer military if a war breaks out. President Reagan ordered the indefinite continuation of draft registration on Thursday.

"Sustainability," Rogers told the committee in closed session last year, "requires an adequate manpower base from which to mobilize. We do not have that manpower base in the U.S. Army today.

"Even with registration in effect," he continued, "and even cannibalizing the late-deploying reserve component units and putting their troops in the individual reserve--the pool of trained manpower--this country will run out of infantrymen, tankers, artillerymen and combat medics before the draft can take over and send me a steady stream for replacements for combat casualties. We have known of this deficiency for years, and every time we have a mobilization exercise such as Nifty Nugget and Proud Spirit it comes out again.

"This country has been putting Band-Aids on that problem," though Rogers said that paying soldiers to re-enlist in the ready reserve "was a fairly sizable compress that will help somewhat."

The former Army chief of staff said that he is "embarrassed that this country, as it beats our allies around the head and shoulders to do more, finds itself in the position that it is going to run out of trained manpower in combat skills before the draft can take over, even if the Congress implements the draft on the first day of mobilization."

Rogers then reminded the committee that the Constitution charges Congress with raising and supporting armies.

"This country has to face up to that deficiency and do something about it," Rogers warned, "if it is serious about being the leader in our alliance. There have been heads of government who have told me that they will not believe our country is serious in its defense efforts until it again brings back conscription. Among those who have told me that are some of the most powerful allies that we have."

Reagan, in announcing that he will continue the requirement that 18-year-old men register for the draft, a step he opposed during his presidential campaign, said his switch "does not foreshadow a return to the draft. This administration remains steadfast in its commitment to an all-volunteer defense force."

Besides deploring the lack of trained reserves to serve as quick replacements, many military officers predict that, unless training facilities are upgraded and supplies for draftees are stockpiled, in any future emergency they would run into the same bottleneck that frustrated them during the Vietnam war.

In 1966, in the early days of the Vietnam buildup, the Army did not have enough facilities and drill instructors to train both draftees and the thousands of men who signed up for six months' training as part of the Reserve Enlistment Program, or REP.

By transferring combat-division personnel to training duty, the Army trained the influx of draftees but could not handle those in REP, prompting charges at the time that it was providing a draft-dodging haven for 120,000 men.

If there should be a repeat of this situation, the six weeks that Reagan said draft registration would save in processing young men for military service would not mean much in terms of getting trained replacements to the field in a hurry, according to uniformed manpower specialists.