WITH THE JOGGING boom of recent years has come a growing public awareness of distance running with the major focus on a single event - the marathon.

If there is a glamor event in distance running, the marathon is it. While almost every metropolitan center has running clubs that sponsor events of varying lengths throughout the year, it is invariably a city's annual marathon that wins the lion's share of media glare.

For whatever perverse reasons, the idea of completing a race of precisely 26 miles 385 yards grips the imagination of many runners. It becomes the motivating force behind rigorous and ambitious training programs.

The event's riveting attraction at first is that of a fraternity (or sorority) badge. It is a rite of passage and proof positive that one is a serious runner.

The marathon is so long in most people's minds that it has an exotic flavor, a mythic air.

The emphasis strictly on the marathon leads to some distorted perceptions. There is a popular misconception that it is special because it is the longest race there is. The marathon certainly is special, if only because so many people treat it that way. But it is by no means the longest race available.

There is another class of events known by the catch-all phrase "ultramarathons," which embraces all runs longer than 26 miles 385 yards. Not surprisingly, such contests have attracted only a limited band of devotees. One of the locales where they have caught on in a marginal way is Washington.

Ultramarathons are the logical next step after the marathon is mastered, although few runners ever proceed past the conjectural stage.

When the concept was first introduced in New York in the early '60s, organizers scheduled 30- and 40-milers. Nowadays the most popular ultra is the 50-mile.

There are problems right off the bat. With a distance nearly double the marathon, it scares most runners from ever attempting it. The D.C. Road Runners partially solved that problem in 1973-75 by holding a fall race at the intermediate distance of 36 miles - the Alexandria Two Bridges Run. It looped around Mt. Vernon and then proceeded north and crossed over to the District before finishing back in Alexandria.

Despite attracting over 80 entrants in its third year, it was dropped from the schedule last year.

There is some talk of reviving the Two Bridges in the future, but for the time being the "shortest" ultramarathoning opportunities for local athletes are three 50-mile races.

The 50-mile run has been an AAU national championship distance for 11 years and recognized standards in the event have developed.

The elite time to shoot for is six hours. Since that mark was first bested in this country in 1966, 44 Americans have gone below it. Four long-time veterans on the Washington running scene are among them - Max White, 26, of Alexandria; Ray Morrison, 31, of Silver Spring; and Ed Ayres, 36, and Phil Stewart, 27, both of the District. White won the national championships in 1974 and in last year's title race Ayres placed third with a 5:46-51 clocking over a rolling 10-lap course in New York's Central Park.

While most 50-milers are held on road courses, a few are run on tracks. Coming up at 6 p.m. Aug. 6 is one, to be contested on a quarter-mile track at Ft. Meade - 200 laps around the oval, finishing under the stadium lights around midnight.

As odd as the format sounds, it at least keeps the runners near their trackside drinks, which can prove critical in the heat of August.

Runners who don't like their laps in 440-yard increments can wait till Sunday, Sept. 25, when a 50-miler in Baltimore takes the form of a dozen laps around Lake Montebello. Both it and the Ft. Meade race can be expected to attract only 15-30 starters.

For those who hate laps of any size there is the mid-November JFK 50-Mile Hike-Run in western Maryland. First held purely as a hike in 1963 with 11 participants, it eventually grew into the largest ultramarathon in the nation. In 1973 the field reached over 1,500, but since has dwindled.

Starting from Boonsboro, it traverses 13 rugged miles of the Appalachian Trail before reaching more civilized terrain en route to the finish in St. James. In 14 years only two men have cracked the six-hour barrier on the JFK course, with Max White's 5:55:30 in 1973 standing as the record.

With the trend toward the metric system, ultramarathons of 100 kilometers (62.1 miles) also have been held in recent years. A variation on this theme each fall since 1973 has been the C&O Canal 100- and 300-kilometer runs, which start at Georgetown.

I have won the 100-km race one time and been runner-up twice, and each time there has been at least on stretch where I haven't seen another competitor for over 20 miles.

Runners who make it to Harper's Ferry have the option of stopping at 100 kilometers or proceeding on to take part in the longest race held anywhere in the Western Hemisphere by trying to run the length of the canal - a mind-boggling 300 kilometers, or more than 186 miles. Few exercise this option and only three have ever made it to the canal terminus in Cumberland, Md.

Alan Price of the District made it in 1974 and Bob Stack of Rockville succeeded in 1975, but both ended up limping, staggering and stumbling most of the way. Only Park Barner from Enola, Pa., has weathered the ordeal in reasonably good shape, but the 33-year-old is famous among runners for incredible feats of endurance.

Despite facing sub-freezing temperatures last year, Barner ran the length of the canal in 36:48:14, including several hours of sleep after he'd run 122 miles, a period of dehydration when his handlers missed a rendezvous point along the wooded trail and about 50 miles of making his way through a pitch-black night with a flashlight!

The C&O Canal also is the site of the newest ultramarathon on the Washington scene - a Sierra Club 100-km. hike each spring. At least for the Sierra Clubbers it is a hike. However, the last two years a few members of the Potomac Valley Seniors Track Club have joined in. And, of course, they've started to run the thing . . .