THERE IS NO justice in table tennis. Just a word with Gordon Gregg, fit and wiry, the picture of a disciplined and conscientious athlete, tells you that.

Gregg runs a couple of miles a day, does stretching and toning exercises, pushups. A math teacher at Montgomery College-Rockville, he keeps his mind as carefully honed as his body.

The red-bearded Gregg is high on the list of talent among players in the Washington Tennis Center's new table tennis club. But he can't beat Monty Merchant and he probably never will.

Gregg's regimen is one he established over the years as his paddle skills developed. He discovered table tennis in 1963 at the age of 21 - "too late to ever be really good," he said.

Nonetheless he is ranked 97th nationally and two years ago won the class C national championships at Oklahoma City.

He works out daily with Aram Avanessi, a former member of the Iranian national table tennis team. Avanessi last year beat the Canadian national champion in the U.S. Open.

And Gregg from time to time can beat Avanessi. But he can't beat Monty Merchant and he probably never will.

Gregg even bought himself a $350 table tennis "robot" - a machine that feeds balls in random directions hour after hour - so he could work on his strokes when no one was around to play with. It helped his game, but not enough.

Who is this Monty Merchant and why is he doing these terrible things to Gordon Gregg?

Merchant is one of the Washington area's newest entrepreneurs. He heads the WTC's two-month-old table tennis operation in Tysons Corner, the first professionally run TT club in the area. And he takes on all comers and never gets beaten.

The heartbreaking fact is that Merchant doesn't even practice. He's not in particularly good shape, he doesn't work out, he smokes, he has a few drinks now and again. Merchant isn't big and he speaks in gentle, lilting sing-song tones. But he's unbeatable.

Last month Merchant, who played for 13 years on the national team of his native India, organized the first tournament of his new club. He drew top players from Philadelphia, Connecticut and other East Coast points.

The winner - Merchant, over David Sakai of Connecticut, who is ranked 24th in the nation.

Merchant finished third in the world championships in Japan in 1969. He has toured and given exhibitions with the greatest table tennis stars of our time. Before he came here he ran a club in Mobile, Ala. For a decade and a half, half his life, table tennis has been his bread and butter.

And like an old pitcher that still can mow down the super rookies in the major leagues, Merchant knows all the tricks. His footwork is ballet-like, full of leaps and twists and thunderous windups for slams. His paddle is never still. He'll precede a simple shot with three of four deceptive twists, so his foe has no idea which spin is on its way.

Merchant's serve is a rapid-fire dialogue of contortions. He serves from the corner and his paddle zips every which-way before the ball takes off.

And the more credible the opposition, the more incredible Merchant's play. Against Gregg, the best at WTC one night last week, he drove the math teacher farther and farther back with each volley and parried each return from table's edge.

After two games Merchant had a trickle of perspiration at his temple. Gregg was huffing and heaving and soaked from the exertion.

The WTC table tennis club meets four times a week. It's a membership deal, but nonmembers are welcome at a charge of $3 per session. Sessions are Monday and Wednesday evenings from 7 to 11 and Saturday and Sunday afternoons from 2 to 6.

There are about 70 members now, ranging widely in age and ability. They operate under a computerized rating system that matches players with others of about their caliber.

One of the regulars is 9-year-old Sean O'Neill, who was away last week watching the world championships in Birmingham, England. O'Neill is ranked second in the nation in the 11-and-under age group.

Nobody at the club is saying so, but it's a good bet young Sean has an eye on Merchant. And if an old pro is an old pro is an old pro, Merchant's watching out for Sean, too.