FOR MOST PLAYERS on the estimated 5,000 softball teams in the Washington area, the average April to mid- July season is quite sufficient.

But what about true zealots with a year-round itch and no invitation to spring training, the shortstop aching to take infield practice, the slugger yearning to swing for the fences right now?

Well, those sports can now come in from the cold -- to a converted Baileys Crossroads warehouse known as Champion Indoor Sports. Described by co-owner Paul Tischler as "the only facility of its kind in the nation," Champion Sports is 21,630 square feet filled with six batting cages, two throwing ranges that measure speed and accuracy, and a regulation-size, artificial-turf infield for softball.

"With the amount of softball players in the area, we thought if this idea could work anywhere in the country, this would be the place," says Tischler. Champion Sports is counting on players' off-season hunger to keep it busy in the cold months, and the scarcity of practice fields in mid-season -- thanks to heavy league use -- to push people to its air-conditioned field in summer.

The field costs $35 per hour during prime time, as does reserving a batting cage. Each is $5 less in non-peak hours. The cages are also available at the rate of 14 pitches for $1. The batting cages can be set for slow pitch softball, fast pitch softball up to 90 miles per hour, or for hardball at speeds between 40 and 90 mph.

Indoor Sports also runs an indoor baseball school, and a weekly slow-pitch hitting league that scores teams of four players each on how close they can come to "the perfect line drive" in the hitting cages.

The early returns have been quite favorable. "We really enjoyed it," said Bob Johnson, who brought out his Class B slow- pitch team, the Phall Guys, and his softball-playing fiance, Bonnie Loopesko. "We got a chance for some infield practice and to loosen up our throwing arms. We had about 10 players using both the field and one cage, and in one hour everybody was very tired and had blistered hands."

Rodney Jenkins, manager of a slow-pitch team in Vienna, figures the facility could give his team an edge early in the season. "If you just go out in the spring, it takes three or four practices just to get back into it," said Jenkins, who visits the cages by himself several nights a week, swinging at about a hundred pitches each night.

"I wish sofball would last all year round," he said. "I want somebody to build an entire field in a dome so we could play all year."

The Northern Virginia Seniors League, a seven-year-old coed league open to men 60-and-over and women 40-and-over, has been using Champion's diamond regularly.

"Normally during the winter, many of the people who play softball will play tennis or do something like bowling," said Bob Swortzell, an organizer of the league. "But you can do those things with only a few people, and this allows all of us to get together. The first time we went out, we had to cut off the number of people participating because we could have only 30 people on the field at one time."

Swortzell said his players have found the winter practice time excellent to concentrate on fundamental areas such as base-running, rundowns and defensive plays, things that are often neglected once spring practice begins outdoors.

Bob Brown, coach of the St. Albans High baseball team in the District, has also been using the field, taking three or four players at a time to work on their fielding and hitting. The infield "really is not big enough to play normal depth for baseball," said Brown. "But it is valuable because you can make a full-sized throw the distance from third to first. They also have a pitcher's mound, so your pitchers can get in the habit of throwing off a mound."

Dave Kyle, another part-owner of Champion Sports, sees the facility as potentially ideal for junior baseball league tryouts. "What are tryouts other than hitting, fielding and throwing?" he said. The advantages to indoor tryouts? The artificial infield would eliminate bad hops and the throwing ranges would measure a pitcher's arm. "And the biggest problem at all tryouts," Kyle adds, "is getting a consistent pitcher for every hitter, and the machines provide that."

Johnson came away feeling his money was well spent, and eager to spend more. "Ten of us rented the field and a batting machine for an hour, which came out to about $7 per person," said Johnson. "That is less than we would pay individually for an hour of indoor tennis."

But Johnson was especially taken with the possibility of a one-hour hitting lesson from an instructor. The $40 lesson, with the instructor's comments on stride and stroke, is videotaped and the hitter gets to keep the tape. "I was dying to do it," said Johnson, "but I don't have a videotape player. Heck, I might do it anyway."

CHAMPION INDOOR SPORTS -- 5629 Leesburg Pike, Baileys Crossroads. 578-3500. Hours: Sunday-Thursday, 10 a.m. to 10 p.m.; Friday, 10 a.m. to midnight; Saturday, 8 a.m. to midnight. Cost: Batting cages and infield $35 each per hour peak time (5 to 10 weeknights and until 10 weekends); $30 per hour all other times. Cages can also provide 14 pitches for $1.

To get there from the Beltway, take I-395 north to Route 7 (Leesburg Pike) West. Follow Route 7 about three miles. Champion Sports is on the left.