Come the first Monday in September, we close our eyes and, for one last day, ignore the inevitable. The summer may be over, the fun may have ended, school and work may loom, but there's still one chance left to ENJOY. Or there is for most of us. For the others, the true meaning of the term "Labor Day" is a purely descriptive one. It's Labor Day. They labor.

For 31 years--that's 31 Labor Days--S. Lowry has been selling his hot dogs, pretzels and pizza on the streets of Washington.

"Sure I get a vacation," he says from his truck near the Hirshhorn Museum and Sculpture Garden. "But not now. Someone has to work while everyone else takes a vacation."

Lowry's family sometimes complains about his habitual holiday absence, but as the hefty man with "LOWRY" informatively tattooed up his right arm explains, "It doesn't do them much good.

"In this business you don't stay home holidays--you're out serving the public. If you stay home, you don't make money."

And although Labor Day is a holiday, the normal rules of business still apply. Lowry won't say exactly where he'll be stationed today or how many pretzels, hot dogs and egg rolls he expects to sell. To commit himself would be against vendor-logic.

"You know why I don't tell you if Labor Day is good for business?" he asks. "Because then you'll print it and the other vendors will read it and they'll come out here on Labor Day. You don't tell your competition what's best."

And, as the summer, and the tourists, disappear, each egg roll becomes more important. National Park Service officer Phil Walsh on duty at the Ellipse says Washington won't see all that many tourists today. "It may be a beach day or a picnic day," he says, "but as far as tourism goes, most people have gone back home to get ready for school."

But no matter how few lost children and exhausted tourists there are to assist, for the sweating servants dedicated to easing the tourist's load, the task continues.

As Walsh talks, a fellow officer is telling four teen-agers, vacant-eyed with confusion, "If you're planning to be lost, you should take these maps."

Walsh nods at the sage advice and continues. "It's just like a regular day. It's one of the things that come with the job. You know about it when you sign on."

Holiday or no, today Cliola Peterson is handling that most essential and intriguing of concessions, the post-card and freeze-dried-ice-cream stand at the National Air and Space Museum. For the temporary summer employe, Labor Day is just another working day.

Then there's that ultimate symbol of summertime ease--the lifeguard. With the pools about to close and the whistles about to be stored for another winter, Labor Day may well be his last chance to bask in the glory of his power and tan.

By the time Labor Day is over, David Trainum will have been out in the sun for 15 hours. Seasonal supervisor for all water activities at Wild World, Trainum checks up on the lifeguards, regulates the water condition, and is responsible for finding Wild World employes dedicated enough to spend Labor Day Wild Wave-side.

"Being a supervisor there, I'm usually the one who has to make them work on Labor Day," he says. "Some of them usually feel sorry for me because I have that job, so they say they'll work, but some just go away. You'd think they would have some sense of responsibility towards the job, but they say, 'Sorry, I'm going away with my family.' "

Unlike Trainum's fleeing lifeguards, some laborers find even the idea of taking Labor Day off incomprehensible.

"I'm so used to it, I don't even notice working on Labor Day," Anna Belle Wills says. Wills is spending today inside one of the red popcorn wagons the Smithsonian stations around the Mall. She's been popping the stuff for 10 years, Memorial Day and Labor Day, summer and winter.

Since June 3, 1981, Concepcion Picciotto has been sitting on the edge of Lafayette Park across from the White House with her disarmament placards. She lives behind the largest of the wooden signs with her friend and fellow protester, William Thomas. The small woman with the tired face and bedraggled hair looks blankly at the mention of Labor Day, as if the words are not familiar.

"Every day," she says, "I am here. There is no rest for me."

But perhaps the work most fitting for Labor Day will be that done by an as yet unknown number of women. On Labor Day, they will be in labor, and doctors and nurses will be laboring along with them. For all of them, holidays don't really exist.

"You just have to make do," says Dr. James S. Powers, assistant clinical professor of obstetrics at Georgetown University Hospital. "It's often difficult for the family, but they just know that Daddy or Mommy, whatever the case may be, may have to be busy on holidays. It's just part of the trade."

Powers has 10 patients due to deliver during September, and he's covering for 10 of his partner's patients as well. Today may be a slow day. It also may not.

"We're thinking of going up to Columbia, Maryland, to the Renaissance Fair," he says, "if my beeper will reach that far."