When Brett Whatcott was a youngster he'd scurry out to the street when trucks from the local National Guard unit drove by his house in Fillmore.

"I would go out and salute them, and they would honk at me," he said. Watching the trucks and jeeps roll by was a big deal in a small town.Today, Whatcott lives in Orem and makes his living doing auto-body repair work. But one weekend each month and two weeks during each summer he dons fatigues with sergeant's stripes and shoots 155mm howitzers with the Utah National Guard in the hills near Fillmore or at Camp Williams.

More than 14,000 plumbers, mechanics, lawyers, doctors, police officers, pilots and other Utahns from almost every occupation imaginable are also part-time soldiers in the the military's various Reserve and National Guard components.

Activity in reserve forces is particularly noticeable this time of year as soldiers embark on annual training missions around the world.

For the soldier, the perceived benefits of part-time military service vary, depending on the individual - extra salary, travel, adventure, training, the chance to perform patriotic service while maintaining a civilian job, and more.

For Uncle Sam, the part-timers are a bargain and an essential supplement to standing military forces. Reservists are also playing an increasing role in the nation's combat readiness, with some reserve units assigned to respond to potential war zones well ahead of their active-duty counterparts.

In a National Security Strategy statement dated January 1987, the Reagan administration addressed the mix of active-duty and part-time soldiers by saying, "The United States must maintain effective and robust Reserve and National Guard forces, trained and equipped at levels commensurate with their wartime missions.

"Today, fully 50 percent of the combat units for land warfare are in reserve components. Reserve units perform important missions and support functions on a daily basis. Their priority for manning, training and equipment modernization is not based on their peacetime status as forces `in reserve,' but on the basis of their direct integration into the nation's operational plans and missions."

Understanding the Defense Department's current reliance on reserve forces is best understood when contrasted with the status of reserve forces during the Vietnam War.

President Lyndon B. Johnson did not mobilize most National Guard and Reserve troops for duty in Vietnam because he wanted to deal with the conflict without interfering with domestic programs and domestic tranquility, said Maj. Gen. John L. Matthews, Utah National Guard adjutant general. "We attempted to fight the Vietnam War without mobilization."

Utah Air National Guard planes flew so many regular missions to Vietnam that the Guard unit was almost as involved as many active-duty units, Matthews said. "We were operating six missions a month in Vietnam without mobilization."

But that level of activity was not the same across the board.

Brig. Gen. James M. Miller, commander of I Corps Artillery, which has its headquarters in Salt Lake City, said reserve forces were underutilized in Vietnam,

and that was "the most terrifyingly destructive thing that ever happened to the reserve components."

When draftees were sent to war it made some reservists feel they had wasted their time during years of military training. The avoidance of reserve units for Vietnam combat tours was so obvious that many draft dodgers actually enlisted in Reserve or Guard units as a way of avoiding combat duty, he said.

"These were bad days for us in the Guard, because you had an awful lot of people who didn't want to go to war, and the way they could find to not go to war was to get into the reserve components."

When the war ended, a budget-driven decision was made to cut the standing military forces significantly and round out war plans using reserve forces.

The "Total Force" concept developed by the Defense Department after the war involved cutting active-duty strength and giving reserve components specific wartime assignments so reserve forces would be mobilized before active-duty units in many instances.

Air National Guard tankers refueled the F-111s that bombed Tripoli April 15, 1986, and Army Reserve troops played a number of roles in the October 1983 invasion of Grenada.

Army Reserve and National Guard troops in Utah, for example, train for deployment in the Pacific - Korea and Japan, for the most part. Under the Army's Capstone program, units train during peacetime for battle areas they have been preassigned to in the event of war.

"That means units know who their wartime higher headquarters would be, and the prime area or theater of operations in which they would be operating," Matthews said.

Some 85 Navy reservists in Utah are pre-assigned the USNS Mercy, a medical ship that is not fully staffed during peacetime. Another 50 are assigned to augment intermediate maintenance activity at Pearl Harbor, for example.

"In my case," Miller said, "my units do not wait for the active guys to go to the Pacific and start fighting."

Miller said he has had concerns that the reserve artillery troops he commands could successfully deploy to Korea or Japan on a large-scale mobilization, because annual training missions in Korea only involve one battalion at a time.

To evaluate the reserve forces' readiness, a massive artillery exercise called Firex '88 is now in progress in Utah's West Desert.

"If I'm going to have that responsibility to load all of those kids on a boat, get them off that boat at Pusan (n Korea) and move them into combat, then I want a shakedown. That's where Firex came from because I get to do everything in Firex, essentially, that I would have to do in Korea."

Firex involves 17,000 artillery troops and support personnel that run the war-time gamut - signal units, supply units, 104 fighter jets, Army Reserve attack helicopters, a hospital, military police and more. Public affairs officers are even publishing a local edition of a newspaper similar to Stars and Stripes each day of the two-week exercise. Some 2,500 of the participating soldiers are Utahns.

Miller said the transfer of specific missions to reserve forces cuts defense expenses - without always cutting the experience level of the soldiers involved. "You can deploy a reserve component unit for 7 cents on the dollar it costs to deploy an active unit," Miller said.

For each active-duty soldier, the government pays a full-time salary, makes housing, schools and recreational facilities available and pays medical, dental and other benefits. "By the time you add that up," Miller said, "it's a terrifying expense.

"In the National Guard, the guy (andles) his own food, his own housing, his own medical, his own dental, sends his kids to school, has an outside job and pays taxes," Miller said.

Some of the more specialized reserve units draw heavily on individuals with prior military service and training, so the experience level is often much higher than active-duty counterparts.

In the Air Force Reserve's 419th Tactical Fighter Wing at Hill Air Force Base, half of the 45 F-16 pilots have combat experience and more flying time than their active-duty counterparts. At annual competitions, reservists frequently score higher than active-duty pilots.

The 145 Marine infantry reservists in Utah, on the other hand, are mostly college students and other young recruits. "The vast majority of the assignments in an infantry unit are oriented towards young Marines who are physically active and able to put up with extreme physical and mental hardships," said Inspector-Instructor Maj. Lewis W. Rollins.

In peacetime, democratic nations tend to reduce their military strength to the lowest possible level, Matthews said. "It's just the nature of the society. There's always the pressure to reduce the military budget and the standing armies."

Hostility against the military develops because the military is seen, in a free enterprise system, as an interference to business, distorting the country's economy and interfering with the success of individuals and with family life, Matthews said.

The Army is allowed a maximum of 740,000 active-duty soldiers. "That's all of our people deployed worldwide," Miller said. In contrast, tiny North Korea has a standing army 860,000-strong. The Soviet Union's is larger still.

"The reserve components have taken on more and more and more assignments as it has dawned on the nation that we could bankrupt ourselves, I suppose, trying to keep up with the Russians, which I don't suppose we'll ever be able to afford to do."