SPANGDAHLEM AIR BASE, GERMANY — THERE'S a roar, then a blur. Afterburner aglow, an F-16 rockets skyward, disappearing in a blink into the low-lying clouds above the rolling German countryside.
Since the end of World War II, such a sight -- an American jet taking off on a training mission -- has been a constant in Western Europe, where more than 300,000 troops were posted at the height of the cold war. Yet the circumstances surrounding the United States military presence in Western Europe have changed completely since communism's collapse five years ago.
For many Air Force personnel here, from commanding general on down, the cold war was a relatively peaceful period.
While US attention focuses on how US forces helped end World War II 50 years ago, however, the US military in Europe today is battling to contain constant strain. The cold war's end has pressed US forces in Europe harder in trying to promote peace than in their previous task of deterring a Soviet invasion.
''The old Fulda Gap business, that was a much simpler threat to plan against than the kinds of threats we're seeing today,'' said Gen. James Jamerson, commander in chief of US Air Forces in Europe. He was referring to the cold war, when the US military prepared for a Soviet attack on then-West Germany through a valley on the border with the former East Germany.
For example, an Iran with medium-range missile capability -- or even a nuclear weapon -- would be more unpredictable and potentially tougher to defend against than massed Soviet armor was, officers say.
''There are a lot of genies out there that can tend to erupt at a moment's notice,'' said Capt. Dave Simon, an intelligence officer.
But ensuring security now is only part of the US military's responsibilities in Europe. Air Force units, for example, are now engaged in three ongoing peacekeeping operations with the United Nations:
* Operation Provide Comfort, enforcing a no-fly zone in northern Iraq;
* Operation Provide Promise, the relief effort of Bosnia-Herzegovina;
* Operation Deny Flight, the enforcing of a no-fly zone over Bosnia.
The longest operation, Provide Comfort, is in its fifth year. There have also been other, shorter-term missions, including Support Hope, the Rwandan relief effort in 1994; and United Shield, which provided cover for the United Nations withdrawal from Somalia this year.
The peacekeeping missions highlight the need to keep US forces based in Europe, even though the cold war is supposedly won, General Jamerson said.
''I don't think anyone foresaw some of the long-term things that we're involved in now,'' he said.
Bring them home?
Jamerson acknowledges that sentiment exists in the US to cut back on military spending and on America's commitment to Europe. But he argues, ''It's far more economical to service those requirements with forces based in the theater, than it is with home-based forces.
''National security strategy ... involves an overseas presence. It then becomes a question of what's the size of that presence,'' he added.
Launched under the Bush administration, and continued under President Clinton, reduction of European force levels will settle at 100,000. In the Air Force's case, that has required severe cutbacks over a relatively short timeframe.
In 1990, at the start of the ''drawdown,'' there were almost 60,000 Air Force personnel based in Europe. That number had been cut in half by November 1994. Bases have been closed and aircraft levels slashed from more than 600 to about 170.
A phrase often heard on the two Air Force bases in Germany -- Ramstein and Spangdahlem, both tucked in the southwestern corner of the country -- is ''doing more, with less.''
The cutbacks, combined with the increase in missions, has caused some grumbling. That's something that much of corporate America is familiar with. But Air Force personnel point out that their business is more demanding and carries greater responsibility, with fewer material rewards.
The greatest strain has been the time spent by Air Force personnel away from their families. During the cold war, US forces in Europe were generally kept close to their home bases. Because there are now fewer bases, troops have to travel farther. Peacekeeping missions in countries on the fringes of Europe keep some units away from base up to 140 days out of the year.
''I accept the fact that I have got to go,'' said Capt. Darrel Ekstrom, an F-16 pilot. ''But it puts a lot of stress on family members.''
After a couple of years of adjusting, however, officers say the situation is beginning to stabilize. ''When you're doing it on a daily basis, you can't help but become more proficient,'' said Lt. Col. Leonard Temoney, ''but we're still stretched very thin.''
Any more cuts, Jamerson and others say, and preparedness and effectiveness could be impaired.
''It's already down to the bone. Any more cuts and you'll be cutting bone,'' said Sgt. Steven Schenck, who helps maintain fighter jets. ''Sooner or later, we'll probably have to go up in spending because the equipment is wearing out.''
The heavy workload is also raising concern among commanders about retaining experienced personnel, as well as recruiting new people.
Sergeant Schenk, a 24-year veteran, said if he had to make an immediate decision to reenlist, he would ''probably stay in and tough it.''
''But in two years, if the tempo doesn't reduce, I might think about it,'' he said of retirement.
Looking at the bases in Germany, the Air Force doesn't seem to be suffering too greatly. Both Spangdahlem and Ramstein have their own Burger Kings and golf courses.
But most say looks are misleading. There is little time now to enjoy creature comforts, they say. ''When I have a day off, all I want to do is vegetate,'' said Captain Ekstrom, the pilot.