Lap swimming has gotten to be quite the thing. More people are swimming these days, more even than are jogging. (About 40 million swimmers, 10 million more than jog.)

As a matter of fact, lots of pools that used to be chock full of frolic are now chock full of lappers, cutting through the water with all the ferosity of a shark bent on a midnight snack.

Perfectly nice people (at least I think they're perfectly nice people -- like me) are suddenly as territorial as a hungry wolf.

As in "get out of my lane or I'll kick you in the head. . . ."

As a matter of fact, it was a kick in the head (early this morning) that prompted these characterizations of my fellow creatures from the whatever lagoon.

Actually, I swim in two pools. An outdoor pool on the weekends and an indoor pool early in the morning during the week. (The outdoor pool is restricted to members of a marvelous swim team before 10:30 a.m. weekdays. Marvelous because they practice their little hearts out and practically never win, but never mind, the pool is theirs and I root, however vainly, for their victories, as does the rest of the neighborhood.)

At the outdoor pool when the swim team hasn't preempted it, there is a narrow lane reserved for lappers.

Lappers often spill over into the big part of the pool, but this temporary territorial encroachment is generally accepted. (Just try and move us.) Everybody at the outdoor pool knows almost everybody else, so things are relatively friendly.

The indoor pool is divided into thirds for early-morning lappers. And it has its own rules, which are somewhat different from those of more crowded hours.

Here are some of the situations likely to arise with indigenous fauna, and suggestions for coping with:

* The Bather. Also known as the bouncer or the paddler. This is not a serious swimmer. This is somebody Cooling Off. Drowning is frowned upon, but a well-placed (accidental) kick should get them out of the swimming lane. There are no Bathers in the early-morning lanes. It is no accident.

* The Frog. The frog kick is probably the most dangerous -- to the other guy -- because you can never quite figure where and when it will land. Frogs have a right to swim, however, so you probably should switch lanes. It makes good defensive sense to perfect your frog kick.

* The Crawler, Splash Variety. This swimmer likes to let you know he or she is there. They beat on the water and if you happen to be breathing (or trying to breathe) when they are beating, you will find you are choking.

* The Crawler, Blind Variety. This swimmer just swims, eyes tightly closed. Heaven help the Bather in his wake. Or the other swimmer. His eyes are never irritated by chlorine.

* The Crawler, Sleek Variety. Not bad as a lane partner, but puts you down because the stroke is so-o-o good. The swim team with the sleek variety always wins.

* The Back Stroker, Foot-Style. This is another big blind kicker. Don't try to breathe. Don't pick a lane he is in.

* The Back Stroker, Long-Armed. This swimmer can take up three lanes and think nothing of it. He usually swims in the middle, otherwise his long arms tangle with the ropes or hit the side of the pool. If you are in an adjacent lane, you will get tangled or hit.

* Sleepers. Mostly these are side-strokers. They are related to Bathers, but don't get in the way as much and are permitted to swim with other lappers.

* Children. Children are never permitted in the lap area. They could be eaten by sharks.

General rules of behavior:

* If there are more than 10 swimmers in the pool, everybody keeps to the right. That way you are only likely to get kicked in the face.

* If there are no more than three swimmers per lane, everybody gets to have his or her own lane. The end lanes, by and large, are more desirable. Which lane you swim in should be determined by when you arrive. First come, first. . . . However, some lappers are adept at edging out others, no matter what. The middle lane isn't so bad unless one of the other swimmers is a Long-Armed Back Stroker. Then you're in trouble.

* If you are kicked in the face or elsewhere tangled, hit or edged out, don't holler. You'll choke. You're in, remember, the water.

* If you kick someone else in the face or elsewhere, tangle, hit or edge out another swimmer, don't apologize. You'll choke. You're in, remember, the water.

And then, of course, you can always jog. . . .