The squad of West German soldiers moved slowly, too slowly, through the barbed wire obstacles, firing plastic training ammunition at fake targets.

The squad leader's voice was not loud enough for all the men to hear, and a follow-up hand-grenade attack by the dozen soldiers might have been fatally uncoordinated if this were the real thing.

But the commanding officer was not unhappy. These men are reservists and this was their first day back at military training since they left active duty 18 months ago.

The men huffing through their paces in this heavily wooded German-American training ground outside Stuttgart are much like reservists and national guardsmen in the United States. The crucial difference, however, is that the West German weekend-warrior is already right on the front line.

As a result, the roughly 800,000 men in West Germany's ready reserve and homeguard forces become an important factor in efforts to assess the overall East-West balance of power in Central Europe.

It is a factor often missing from published assessments of how well the West could meet a quickly mounted attack across central Europe by Soviet-led Warsaw Pact forces.

Like reserves anywhere, the West Germans have forces varying quality. On balance, however, the West German reserves are formidable.

More importantly, they are the only large, reasonably well-equipped and experienced force available within the NATO alliance that can be mobilized fast.

Brig. Gen. Wolfgang Altenberg, deputy assistant chief of staff for the West Germany army, says this country's 495,000-man active duty armed force can be roughly doubled within three to four days by a call-up of trained reservists.

West Germany's active duty ground army of almost 350,000-men is equipped with enough tanks, guns and underwear to handle a rapid expansion to twice its peacetime size.

The question of the West German reserves has taken on added importance recently because of growing fears in some circles that Warsaw Pact strength along the front lines is getting so high that the Soviets could launch a surprise attack virtually from a standing start, with little or no warning time available to the West.

Senior commanders generally do not seem to believe the Soviets would actually risk such an undertaking, and others challenge whether it could be done with much surprise. But such fears nevertheless raise questions about whether the 15-nation NATO alliance could respond in time.

If a battle seemed to be in the making, however, it would be fought first on German soil and the Bonn government can call up its reserves to protect its territory with little or no warning time.

While even a million-man West German force, plus allied troops stationed here, might not be able to contain indefintely an all-out Communist attack, the addition of the reserves might help blunt such an attack long enough for other reserves from the United States, Britain, Canada and other European allies to reach a German battlefield.

The East, of course, also has reserves. But they are farther from the front and mobilizing them would give the West more warning of an impending attack.

Unlike the United States, West Germany still has a conscript army. Men become eligible for the draft at age 19 and generally serve 15 months on active duty. They become reservists afterward, required to train between one week and a few weeks each year until they reach 32. For officers and noncommissioned officers, the reserve obligation is longer.

Roughly 30,000 of the reservists are on call on just a few hours notice. These are specialists that go immediately into combat units that move toward the eastern border. They form part of a covering force aimed at allowing the fuller mobilization to continue.

The bulk of the reservists go into the army. They go as individuals into existing active units rather than into service as complete reserve units.

But 240,000 men would go into homeguard units. These are different from the rest of the reserves because they are exclusively under West German, rather than NATO, control, even in wartime, though the West Germans can allow them to be turned over to NATO if needed.

Many of the men are simply meant to guard key facilities behind their own lines against sabotage.

But there are also six 8,000-man homeguard brigales in wartime that are both mobile and equipped with 64 tanks plus self-propelled mortars in each brigade.

These units are specially concerned with defending against the six. Soviet airborne divisions that could drop behind the lines. While the homeguard tanks are older U.S.-built M-48s, officers here point out that the Soviet tanks that would be dropped by parachute would also undoubtedly be light and not necessarly better than the M-48.

Later this year, the West German Defense Ministry is expected to announce a further streamlining and requipping of the reserves along the same lines as a new army reorganization.

The West Germans are very proud of their high "teeth-to-tail" ratio, which means a high percentage of actual combat troops to those in support. They have squeezed 36 combat brigades out of their active duty forces, a ratio considereably higher than the U.S. army's.

But as Gen. Altenburg points out, "we are not going to Siberia. There are bakeries and filing stations on every corner and lots of hospitals around. We don't need our own in the army."