In the half-light of the old Hillcrest Heights gym, the solitary boxer looked ghostly: Perspiration matted his long blond hair and soaked the white thermal underwear worn to sweat off an extra pound. Darting around a makeshift ring, his feet skimmed across a grimy tarpaulin floor held together by long patches of gray tape. When he exhaled--which he did with every punch--the hiss sounded like steam escaping from a radiator.

At 23, Neal C. Allen is no stranger to the boxer's regimen. He goes through a punishing routine of running, workouts on heavy and light punching bags, sit-ups, jumping rope and sparring with an ease acquired in 14 years as an amateur fighter.

By last week, however, the daily training had taken on a certain urgency as Allen prepared for his professional debut this Saturday. The youthful days of Boys Club and Golden Gloves tournaments in Prince George's County were left behind, lost in mind-numbing drills for the upcoming four-round bout with a fighter from Philadelphia.

Boxing is bigger than ever in Maryland and especially so in Prince George's, where amateur boxing programs have mushroomed for youngsters, inspired by real-life and celluloid heroes like Sugar Ray Leonard and "Rocky."

"Boxing has always been popular around here, but it's really taken hold in the last three or four years," said Truman Tuttle, a Bowie resident who has watched the local boxing scene for more than 15 years.

Ten years ago, 20 private or municipally sponsored boxing clubs dotted the Baltimore-Washington axis; now there are 50, Tuttle said. In 12 years, the number of entrants at the regional Golden Gloves tourney that Tuttle directs has nearly doubled; 425 young fighters competed in the tournament last weekend. Many of those amateurs came from Prince George's, whose low-income neighborhoods have spawned teen-agers who regard the sport as a glamorous road to success, Tuttle said.

"They see fighting as a way of getting out," said Tuttle. "They see other people making money and want to do the same."

The dream of big-money fights as a professional is the fire inside Neal Allen, who received his first gloves shortly after he learned to walk. An inch under six feet, Allen is a wiry 147-pound welterweight, a soft-spoken man regarded in local boxing circles as a reliable, if unspectacular, fighter.

"The training isn't a lot of fun, but boxing is a great opportunity to make something of yourself," Allen said last week during a workout at the Hillcrest Heights Boys Club gym. "That's what it is: the big dream, the good money."

As a white man in a sport dominated locally and nationally by blacks, Allen will be able to attract bigger crowds than he might otherwise, he said. "I know I can make money. I'm a draw," he said.

"I'm white and I'm good. The potential is there for some decent money."

At first, the earnings will be small. Allen, who will pick up less than $500 from his fight on Saturday in Novak Field House at Prince George's Community College in Largo, said he will fight professionally for a maximum of three years--a point when many professional fighters are at the peak of their earning power.

Yet in that short time, "if I get some good fights--title fights--there may be no limit to what I could earn," he said.

Allen has no illusions about the difficulty of duplicating the careers of Leonard, junior welterwight Aaron Pryor or the three other world champions--light heavyweight Mike Rossman and heavyweights Ken Norton and Leon Spinks--who have fought or trained at the Hillcrest Heights gym. Nor do those who know him. "The odds are very long for a fighter to make lots of money--unless he's very good," said Tuttle, the head coach of the Hillcrest Heights boys club.

"Neal's got the right background: He went through the amateur program before turning pro," said Tuttle. "He was a good opponent. He's got a lot of determination. With that, he can go a long way now."

Allen compiled a 252-23 record as a novice and junior fighter, earning four Golden Gloves titles and three Amateur Athletic Union titles. Discharged last year after four years in the Air Force, he lives with his wife of four years, a telephone company employe, and their infant daughter in a trailer park in Davidsonville. When he isn't baby-sitting, Allen said, he trains.

The fighter shuns alcohol, tobacco and coffee and trains six days a week. Sundays are spent with the family, sometimes as a Sunday school teacher at their Methodist church.

Most days start at 7 a.m. with running in the morning and exercise between three square meals. In recent weeks, Allen's sparring and gym workouts at Hillcrest Heights have lasted until 9 or 10 at night--always under the scrutiny of his father, Walter, a former amateur fighter who now works full time as Neal's trainer.

The senior Allen is his son's caretaker and chief critic. He sets Neal's daily schedule, holds the water bottles and towels, applies petroleum jelly to his son's face before he spars. "We're very tight," Walter Allen said. "When he's gone on the road, he's had to fight for other trainers, but it never worked out. He can't fight for nobody but me."

The son likes the arrangement. "With Dad as my trainer, I know he won't shaft me as some trainers have done to their fighters," Neal said. "Plus, the family is behind me all the way on this. That helps."

Also supporting Allen is a coterie of friends and old boxing hands--and a newcomer to the sport: his manager, Dovie Trevino, the wife of Hyattsville lawyer Hal Sullivan, who is promoting a series of monthly fights at Novak Field House. "When I saw my first fight, I thought boxing was bloody and brutal," Trevino said. "But there is an art to it. Neal is very ambitious. And he has the desire it takes to be a winner."

Allen, who said he has never been knocked down or out while an amateur, remains unperturbed by the attacks on the sport that followed the death last November of Korean fighter Duk Koo Kim, who suffered a cerebral hemorrhage during a championship fight. "People who don't know boxing see it as two guys who get into a ring and start swingin' at each other," he said.

"But that's not it at all. To me it's a sport. To be a good boxer you have to use your brains. When you get into that ring, you have to know how to avoid punches. You have to know the different moves, the different styles, the different techniques."

Allen's last fight was a year ago, but the past three months of practice have primed him for the Saturday bout, which Trevino expects will be seen by 2,500 people--a full house at the Novak arena.

"I've got the desire to win," Allen said as he drew on thin gloves to pound on a lightweight speed bag. "A fighter has a lot more drive when he's fighting for money."