WITH THE DAYS growing shorter and a hint of fall in the air, the heat-weary jogger's thoughts return to lunch-hour running.

Nothing quite matches leaving the office at midday, while coworkers stoke up on calories at Burger Haven, and running far, far away from it all. A quick shower and you're ready for whatever crises the afternoon had to offer. It's like taking a vacation every day.

Washington is ideally suited for lunch running it's almost as if Pierre L'Enfant designed it that way: The vast expanses of the Mall; scenic Hains Point and the Tidal Basin; the bridges - Memorial and 14th Street - and their connecting bikepaths that provide sweeping views of the Potomac; the serene stretches of the C&O Canal towpath.

For the lovers of deep woods and hilly trails there's the short jog over to Roosevelt Island or to the winding paths of Rock Creek and Glover Archbold parks. The variety is such that you can run a different course every day of the week.

As a class, lunch runners tend to be less solitary and ascetic than morning joggers, who are inclined to boast about "getting it over with." Lunch runners eschew the dubious pleasures of moving in predawn chill or in pitch darkness on winter evenings.

"I can't stand the idea of getting up at 5:30 in the morning to run," said Phyllis Gibbel, a U.S. Customs employee who runs regularly at lunch with a woman partner. "I can't even walk in the morning, let alone run. By noon I feel loosened up enough to exercise. In the evening it's too easy to put off doing it."

Lunch running is a relaxing experience to be savored either alone or in company. There are lunch running partnerships like Gibbel's larger groups that meet at pre-assigned times and places, informal groups that wax and wane as individuals are available, and pickup pairs and groups formed at central locations such as the YMCA or the Pentagon.

Women runners never lack for male companions if they want them. A common sight these days at the Tidal basin or the Mall is an attractive woman runner surrounded by a pack of attendant males. The subway had proved a boon to running courtships: a Capitol Hill runner describes taking Metro to meet his girl-friend in Dupont Circle for a lunch run.

Unfortunately, lunch running is not yet a sport for the masses. It requires both time and proper facilities, which can be in short supply. While there may not be enough hours and showers to please everyone, the determined runner can usually cope.

"If you really want to do it, you can find the time, and if you really want to do it, you can find a shower," contends Mike Eosenzweig, who conducted a survey of lunch running for the D.C. Road Runners Club last winter. "Just stand on the Mall at noontime. You'll count hundreds of people running in all directions. Every one of them worked it out differently."

The elite among lunch runners are executives and professional with private washrooms who can take off for as long as they want and find a shower for their use on their return. Not quite as privileged are bureacrats and businessmen who have access to communal showers where they work. Further down the ladder are runners who have to walk to the YMCA or other health clubs to shower and change. Trekking back and forth to the Y can use up a normal lunch hour - even without a run.

At the bottom of the pile are wokers with fixed hours and no place to shower and change. They need the most initiative to become lunch runners.

But where there's a will, there's a way. For every obstacle, there's a story of someone who overcome it. A short lunch hour? Offer to come in early or work late to make up the lost time. Show you boss that you're more productive than someone who returns from a two-martini lunch.

It helps to have a sympathetic supervisor.

"I told my boss I'd work an extra hour in the evening," said Rosenzweig, a mathematician at the Federal Energy Administration who runs up to 10 miles daily at lunch. "But my boss runs, and his boss runs too, so it was easy."

Not everyone is so lucky. One government worker required a memo from her supervisor before she was allowed to take a 90-minute lunch break. She comes to work a half-hour early and runs her four to six miles at a fixed time every day.

"My boss runs a mile in the morning, so he understands," she reported, "but I'm sure the director thinks it's silly."

Shower stories are legion. Perhaps the best involves a runner who convined his agency that it needed a shower for s afety reasons.

"Someone might get a speck in his eye or something," he explained. The shower arrived but sat uninstalled in a carton. Again, the runner rose to the challenge. If the shower wasn't installed, he argued, someone could complain that the agency had wasted government money in purchasing it. Shortly thereafter workmen ripped out a toilet and installed the shower, which the runner enjoyed in privacy for months until others began running, too.

Government agencies vary widely in the availability of showers and changing rooms. Some have extensive facilities for each sex; others have only a single shower room so men and women have to take turns. More than one woman runner had forgotten the schedule and surprised a roomful of naked males.

One woman found a private washroom for her use after men runners complained that their lunch schedules all revolved around her shower habits. (For information on showers for government workers, call the Inter-Agency Jogging Council, 223-9548.)

A little enterprise will often uncover a shower used only by janitors and maintenance men usually willing to share it. Marathoner Ellen Wessel recalls using an uncurtained shower in a HUD basement, guarded by female janitors. Dave Gottlieb, a pioneer lunch runner, tells of standing in a washtub in the janitor's office.

Finally, there are those wo argue that a shower immediately after running is not necessary for health or social well being - at least not during the cooler months of the year. For what it's worth, three women runners interviewed all insisted that toweling off, plus a sponge bath in the ladies room, is sufficient under normal circumstances. Perhaps someone should sponsor a consumer acceptance survey to settle the argument . . .