WHEN ED WROTH flew back to Washington from a sports conference in Georgia one evening this week, what struck him, as his plane circled the city in the gathering night, was the incredible number of softball diamonds that punctuated the pattern of lights below.

"They just went on and on. There seemed to be nothing down there but streetlights and ballparks, mile after mile."

Wroth might be expected to notice such a thing because he's up to his ears in softball half the year as a recreation supervisor for Montgomery County. The reason the rest of us should be expected to notice the softball mania that has seized Federal City is that there's a game going on just about every afternoon and evening on virtually every one of the hundreds of softball fields in the city and suburbs.

Slow-pitch softball has become far and away the most popular organized sport in the region, according to the people who should know. "It would be even more popular if we had more ballfields available," said Jack Ross, softball czar of the D.C. Recreation Department. "We've got people playing on every little open patch in town, and lots more waiting. We just can't squeeze in any more games."

On most lighted fields in the area there are two or three games a night, every night, and there are frequent marathon round-robin tournaments that run round the clock through a whole weekend: Scores of teams playing hundreds of games, supposedly to benefit medical research or some other good cause, but mainly because to the American ear the two magic words (after tax refund and not guilty) are play ball!

Hereabouts, we play ball to the tune of at least 50,000 softball games a season, which can run from April past October, counting only adult games (age 18 and up, sometimes up to the 70s) sanctioned by recreation departments.

"We sponsor about 10,000 games a year here in Montgomery County," Wroth said. "It may amount to twice as many when you add in the cities of Rockville and Gaithersburg, and no end of business-sponsored leagues, including teams that play as many as 120 games a year. Now, if you were to include the games they play in the schools. . . ."

The number of area players has doubled and redoubled in recent years, growing much faster than the general population. Some of the explanation has been the baby boomers, whose age cohort now commands the 25-to-35 age bracket that embraces the most active softballers. Some more of the explanation is the current obsession with physical fitness. But a whole lot of the explanation is sex.

Sex. As in the opposite sex, the fair sex, the -- let's face it -- weaker sex. Coed slow-pitch is the fastest-growing segment of the sport, according to most area officials. Your modern woman's not satisfied to sit in the stands and cheer on her man anymore; she comes to play, and there have been radical rule changes designed to minimize the average man's advantage in size, power and speed over the average woman.

The rules vary in each jurisdiction. In the admittedly semi- chauvinist Capitol Hill League, women players may still be outnumbered, by as much as 8 to 3; all other local leagues require equal numbers of men and women on the field (usually 5 of each) and they must alternate both in fielding positions and in the batting order.

In Montgomery County's "reverse co-rec," men who throw righthanded must bat lefthanded, and vice-versa, at the option of the opposing manager (who is allowed to change his or her mind twice, even between pitches). In Arlington, if a man draws a walk, the woman batting behind him may elect to walk also, making it more perilous to issue free passes to power hitters. In Alexandria and Prince George's County, and probably in most other area leagues next season, male hitters take their cuts at semi-dead balls 12 inches in circumference; women get to pound an 11-inch rabbit ball. PG also allows dual designated hitters, so that there can be a 12-person lineup.

Alexandria also has the most unusual rule of all: every player bats every inning, never mind the outs. If the 10th batter draws a walk, the baserunners advance and the same batter starts a fresh count.

"We all tinker with the rules to try to even things out," said Alexandria Recreation's Jim Dunn. "The idea is to make the woman's contribution a real one, and it works. The men more or less neutralize each other, and as often as not, it's the women's play that decides a game."

Which is not to say that anybody forgets for a minute that some of the players are male and others are female, and vive la diff,erence.

"It's the best way to meet people in this town," said Gary Caruso, a congressional staffer and commissioner of the Capitol Hill League's B "as in beer" Conference. Caruso captains the Yellow Journalists, a team largely composed of House Democratic press assistants. "People are always getting married to teammates," he said. "This fall, for instance, our left fielder's going to marry our first-base person. Beyond that, you meet trade organization people, committee staffers, all sorts of people. It's one of the best ways to get into some types of Washington circles, and that's important, because the city's so transient, it's hard to make connections."

The B Conference is more free-swinging, in several senses, than the Hill league's more highly structured A conference, Caruso said. "Generally we just let teams play who they like when they like, and we're moving a little faster on the woman thing, equalizing it more. The, ah, imbalance could be just the nature of the beast up here."

A shortage of experienced women players probably accounts for the rocky time Caruso's team has had in Arlington league play this summer. The Yellow Journalists, finalists the Hill playoffs last year, have been hard-pressed to break even when they venture across the river. Last week, for instance, they were pounded by the Arlington Wrecks in a grudge match that grew out of the YJ's less-than-gracious demeanor during an earlier one-run win over the same team.

"Yeah, well, we play hard," Caruso said.

That night, the Wrecks played harder, especially first sacker Ave Neumeister, who -- as a South Pacific veteran said of the Japanese warrior -- is "not so very big but is wound up very tight." At the moment Neumeister actually is two tiny people, one of them a player to be named later, and looks like she, er, swallowed a softball. She and husband/teammate Don Neumeister managed to time things so she should be able to make it through the playoffs and be ready to suit up again in the spring.

Johnny and Margaret Gibson, on the other hand, got out of sync this season, so that she's almost due with their fourth child while their Gibson's Korner team, named after the family stor in Alexandria, is relying heavily on enthusiasm and Ace bandages to stay in contention in the city's top coed division.

A very large proportion of the enthusiasm is supplied by Vic Price, 34, a massively muscled former minor leaguer whose voice is even mightier than his bat. "Let's get a little UPSET!!!," he roars, and everybody for blocks around does, although Price, who is also a world-class armwrestler, radiates the gentle geniality often found in men of extraordinary strength.

Price, a member of last year's men's state championship team (and MVP of the tournament), runs Vic's Tree Service by day and plays softball by night, nearly every night. "He doesn't own a saw, he just pulls the trees up by the roots," a teammate said. Price demurred. "I love trees," he said. "I love being outdoors and working for myself."

But most of all he loves playing ball, loves it and plays it with a quivering, roaring intensity that intimidates even teammates who know that, as one said, "There isn't an ounce of mean in him. He's the sweetest man I've ever met."

Tell that to the umpire who last week called Price out for being out of the batter's box when he hit an apparent homer that almost made it to the infield of a diamond across the way.

"Stepped on the plate?" Price roared, dancing up and down on the basepath so that heaven and earth shook, along with the ump and the backstop. "Stepped on the plate?" He strode back and forth in a seeming frenzy, yanking at his curly blond shoulder-length hair so hard it seemed likely to come away in his fists.

Then he stopped and stood with his hands folded in front of him. "Excuse me, Mr. Umpire Sir," he said. "I want you to know that I am not questioning your judgment, Sir, but that's a K (strikeout) you have awarded me. A K. I just don't know how to handle a K, Sir. Pardon my behavior."

Then he was off again, hopping up and down and gesticulating wildly as he retired to the bench. "A K, a K, a K, Victor you pulled a K, you idiot."

Price kept on until the woman behind him in the batting order stepped up to the plate, at which point he seemed to forget about himself. "Get a little UPSET!!! he hollered joyously, and the game went on.

It also went wrong: The opposing shortstop, a woman the Gibsons had until that night regarded rather lightly, cleanly fielded one hard smash after another, cutting down runners and killing rallies like Honus Wagner. Once she erased Dave and Sherry Marion in a double play before the innocent eyes of their son Curt, 22 months.

The Gibsons hung in there but came up short, in spite of some excellent plays by such as rifle-armed rightfielder Marybeth Daucher, who threw a 200-foot strike to second base that wiped out a runner everyone had assumed would reach third standing up. That drew the headiest applause of all: a long moment of stunned silence.

"No, they don't throw like girls, do they?" grinned Gibson, taking what pleasure there was to be found from the 13-17 loss, which was fairly clearly attributable to errors and indifferent hitting by the men. And for all their cheerfully obscene badinage and the easy fraternization with the enemy, they took it hard. "Getting beat's bad enough," said Annette Costa, a topflight player from District Heights, "but I purely hate to lose."

"It's a totally different game when you play with women," said Price, a Langley High School graduate who spent some years in the Pittsburgh Pirates farm system. "Women play really hard. And in coed, with no fences, you have to be able to place the ball, because the outfielders can back up forever."

Soaking up pitchers of iced tea in a pizza parlor after the game, Price said his energy and enthusiasm may have been what kept him out of the big leagues. "I'm always like this, I've always been like this, and I always want to be like this," he said. "When I was playing professional ball they thought I was on drugs, because nobody else played like me.

"I've never had anything to drink or smoke, never have taken any kind of drugs. I think I'd burn right up if I did, because I get so high naturally on adrenalin. I get high at every game, and then afterwards I'll come down really flat and then I go home and read for a couple of hours, or play the piano or my guitar.

"Stickball, baseball, softball, it's all the same game, and I love it. I played in high school and college, played everywhere all the time. But then when you get to the professional level, all of a sudden you're not a human being anymore, you're just a piece of equipment. If you get hurt, or they get tired of you, they replace you, that's all.

"But this game, this is still the game. Obviously the players aren't as good, but they play just as hard -- at least as hard -- and that's what counts. And here, if I get hurt, I can go and sit down. Nobody's going to call me in and say, 'Vic, we're sending you home.' "