As hard as it is to believe, lots of people are arranging entire vacations around wearing themselves out in Washington, Boston, New York, Los Angeles, London, Honolulu, Moscow, Berlin, to name a few.

Why people want to exhaust themselves in the name of fun is another story; but suffice it to say that marathoning, as Capt. John Thorson, assistant Marine Corps Marathon coordinator, puts it, is "no longer a novelty; it's a lifestyle."

Registration for our hometown marathon is up about 2,000 over what it was at this time last year, which means officials expect to reach the 13,000 limit soon. And this is despite the Persian Gulf crisis, which is occupying a lot of Marines, some of whom might otherwise be running Nov. 4.

Or maybe numbers are up because of the crisis. "I have a gut feeling that there's some red, white and blue coming through here," says Lt. Col. Lorraine Goodrich, public-affairs officer for the marathon.

Or more bleakly, maybe some people want to get in a marathon before it's too late. And, of course, there's nothing like a 26-mile run to forget the specters of both war and recession.

Another reason to run a marathon -- and if only more people would latch onto this one -- it's a guaranteed way to stay off a drug habit for a few hours. And if more addicts ran marathons, or just ran, they might decide they like their own body's opiates and endorphins better than the street-bought kind. And they're a whole lot cheaper.

Which brings us to this year's theme -- "A Marathon for a Drug-Free America" -- the Marine Corps' hopeful call to exerting the best that's within us.

Whatever the reasons, the Marine Corps Marathon -- or "the people's marathon" as it's called -- continues to grow in popularity and is the third largest in the country, behind New York and Los Angeles. It's also considered the best organized, the best staffed medically and the most supportive to first-timers. (About 2,000 Marines and sailors from Quantico and 1,500 civilians will be out there as volunteers on the course, which winds through Arlington, Georgetown and the District.)

Unlike other major marathons, there is no prize money. But the route itself is considered a prize, a tourist's dream, past the Capitol, the White House, Jefferson and Lincoln memorials, the Pentagon and the Kennedy Center. "You're running near all those things that most people see only on the evening news," says an Ohio marathoner. "And it's a big thrill."

When Marine Corps Commandant Gen. Al Gray fires the starting pistol at the Iwo Jima Memorial -- followed by a roar from a 105mm howitzer -- two men in that sea of 26,000 running shoes will be stepping off on their 15th consecutive Marine Corps Marathon. They haven't missed one since the first in 1976, and have finished all of them, too, which neither considers a big deal. Maybe after 14 marathons you get that way, and maybe it's because running is as much a part of their daily lives as getting up in the morning.

John Marshall of Sandgates, Md., was 35 when he did his first Marine Corps Marathon, and Charles Stalzer of Mount Vernon on the Potomac, was 47. There were 1,500 entries, and about 1,000 finished.

"We had a lot of fun," says Stalzer. "On that first one we went through Old Town Alexandria. And because there weren't so many runners on those first runs, you could spot someone up ahead and set a goal of reaching or passing him."

Stalzer wore Keds sneakers to run in, and he remembers clearly the day his wife called to announce that a store specializing in running shoes had opened. He also recalls a time when the only qualifying necessary to get into the Boston Marathon was the purchase of a 50-cent American Athletic Union card to show amateur status.

His best time for the Marine Corps Marathon was 3 hours, 29 minutes, and this year, at 62, he hopes to finish under 3:50. He's been running about 50-60 miles a week the last couple of months, and runs about 35 miles a week when he's not in training, much of it on his noon hour. (After he retired as a Navy jet pilot in 1975 he went to night law school and passed the Virginia bar. He's now in procurement -- he buys rail cars and buses -- for Metro.)

But back to his training; he believes firmly in the (controversial) pre-marathon run (at least two weeks before) of around 26 miles. "It's important," he says, "that the system understands the 26. And you have to train a little bit running on empty and with some stiffness that you're bound to have on marathon day.

"Of course," he adds, "everyone is an experiment of one."

Running's place in his life generally?

"If you are a time-limited person," he says, "running is probably the best activity per minute you can have. If I don't run for a few days, I don't eat and sleep as well. I don't feel comfortable; there's just a general drop in my feeling of well-being."

Stalzer, 5-7, 132 pounds, doesn't wear glasses, which he attributes to running's effect on his circulation. "If I don't run for three days, my eyes get a bit blurry."

Marshall, who is supervisory engineer for the Naval Air Test Center, Patuxent River, and deputy program manager for the Unmanned Air Vehicle (UAV) program, also says he feels uncomfortable after three days without running.

"I solve a lot of equations while I'm running," he says. "My theory is that a lot of oxygen goes to the brain and promotes thinking. I'm usually deep in thought, and it's not about running."

His "basic modus operandi" for the marathon is "to see how little I can train and still finish feeling good."

His regular marathon training is six to eight miles, five days a week, with his longest run about 10 miles. His best time over the years was 3:19, and this year -- at age 50 and 5-7, 148 pounds -- he hopes to repeat last year's time of 4:39. He'll probably walk/run the last three or four miles.

He's passed through "the wall," he says -- a point where just keeping going takes supreme exertion or may be impossible -- a couple of times during the marathon. The crowds, the John Philip Sousa marches and the Iwo Jima Memorial all have helped to pull him through.

And more than once when glimpsing Felix de Weldon's sculpture, he has thought of such things as war and the fact that "a lot of guys go through a lot more than this. This little {marathon}, this little thing is nothing. I can do this." Watch Words

For marathon watchers, some details to exchange with that person shouting on the sidewalk beside you:

About 60 percent of the runners are first-time marathoners.

About 80 percent are civilians; 20 percent from the military.

Ratio of men to women: about 5 to 1.

Because of the crowd (13,000 runners), the last person over the starting line will be 2 1/2 minutes behind the first.

Among competitors are about 20 wheelchair athletes and 15 blind runners.

Among about 30 foreign runners are two from the Soviet Union: Olga Markova, 22, who hopes to do the marathon in 2 hours, 36 minutes, and her coach, Gregory Vinjar, 43, who won the 1975 Soviet National Marathon in just under 2 hours, 16 minutes.

Best Marine Corps Marathon running time: 2:14:1, by Jeff Scuffins, Hagerstown, in his first marathon in 1987.

Best wheelchair time: 1:54:23 by Ken Carnes, Morningside, Md., in his third race, last year.

Cost of staging the marathon: about $200,000, all from entry fees ($17; $25 for late registration).

Everyone crossing the finish line will be wrapped in a foil "space blanket," handed a cup of chicken or beef broth and festooned with a ribboned medal.

Anyone who has not reached the 23-mile mark by 2:30 p.m. (5 1/2 hours after the start and just before the 14th Street Bridge) must board the straggler bus. No exceptions, the pamphlets declare sternly, will be made.

And all this time you thought the marathon was 26 miles? That was the original distance with the first marathon run at the Olympic Games of 1896, from the village of Marathon to Athens.

The distance changed in the London Olympics of 1908 when the race began on the lawn of Windsor Castle so the royal grandchildren could see the start. The distance to the finish line at Shepherd's Bush Stadium was 26 miles, 385 yards. And that has remained the official marathon distance ever since. Getting Down to Basics

For beginning marathoners, some basic reminders from David M. Brody, founder of the George Washington University Runner Clinics and now an orthopedic surgeon in Norwalk, Conn.:

Don't do anything new on marathon day that you have not tried during training. The big day is not the time to experiment with anything, from different socks to different food.

Be prepared for hot or cold weather. The temperature on marathon day could be anywhere from about 35 to 85. (Precipitation averages about .07 inch on this day.)

Don't take the carbo-loading edict too literally, like one poor fellow who ate two loaves of bread the night before and had to drop out of the race. Emphasize carbohydrates in the days preceding the marathon, but don't stuff yourself. You may want your main carbo-loading meal at lunch time the day before, followed by a light supper of easily digestible food. By now you should know what works for you.

When you get to the drink table, take two cups of water. Drink one and, if it's hot, dump the other one over your head. Keep drinking every chance you get.

Remember that you want the water inside, not outside. Don't get your feet wet, or you could get blisters.

When you want to walk, walk. Walking is not a shameful activity.

If you still haven't run 20 miles, the latest you should -- and still have time to recover -- is next weekend. Take it slow and easy, remembering that Brody would be more comfortable if you already had done your long training runs.

If you develop an injury that lasts more than three days, get professional help.

Remember you won't lose anything if you do some alternative training, on the Stairmaster 4000 or the NordicTrack, for example. Also, consider that 30 minutes of water running is comparable in exertion to three miles on land; one mile of swimming equals four miles of running; six miles of biking equals one mile of running.

Most runners, says Brody, can do 20 miles. The rest will depend on hydration, training background and, he adds a bit ominously, courage.

But if you cramp up," he says, "go lean against a tree or a Marine. They'll be everywhere."

Need more details? Brody, medical director for the last 12 Marine Corps marathons and an 11-time marathoner himself, will present the last of his free, pre-marathon running clinics, 7 to 8 p.m. Friday at George Washington University's Ross Hall, 2300 I St. NW., Room 101.

He'll also offer last-minute advice at packet pickup headquarters, the Sheraton National Hotel, Columbia Pike and Washington Boulevard, Arlington. The symposia, geared primarily to the first-time marathoner, are at 7 p.m. Nov. 2, and 4 p.m. Nov. 3, the afternoon before the race, when Brody will all but take you by the hand and lead you over all 138,435 feet of the way.

For still more information: Jeff Galloway (author of "Galloway's Book on Running") will speak at the pre-race-night pasta dinner at the Sheraton National Hotel.