"Six clubs," said the man dressed all in gray, but it was a terrible mistake, a country club-level blunder that cost him the Maryland Open Team championship of bridge. He meant to say "six hearts," and his five kibitzers in the rather frumpy ballroom of the Baltimore-Washington International Airport Holiday Inn knew it.

His partner and girlfriend, diamond-bedecked Lea Du Pont, of the Delaware chemical Du Ponts, was openly diappointed, but the man dressed all in gray took it in stride. "I have made my mark," he said.

Benito Garozzo has indeed made his mark. From 1959 to 1969, he was the mainstay of the famed Italian Blue Team, which was to bridge what the Boston Celtics were to pro basketball, winning 13 world championships in that decade. So what was he doing playing in a state tournament in the bleak suburbs of Maryland? And what was he doing playing so badly?

The answer to the first question is simply that Garozzo has always loved to play bridge 88 any time, anywhere. As to why he played so badly, Garozzo said, somewhat wistfully: "After 50, your reflex to see a situation at the table slows down. And I am 53, my friend."

With Garozzo in decline, the world order of bridge is changing. Now, perhaps, it is the United States on the verge of a dynasty. The Americans have won the last three Bermuda Bowl world titles, and will be gunning for a fourth this October in Rye, N.Y., with a young team that is considered not only good, but hungry. "October. Rye. World championships. cI'll be ready," says Jeff Meckstroth, the brilliant young American star.

Meckstroth's recent bridge record is as illustration as his sentences are brief. A 24-year-old college dropout from Upper Arlington, Ohio, Meckstroth had been an up-and-coming bridge star for many years. He sealed his reputation with a performance at last fall's national championships that bridge folk likened to a baseball player leading the league in batting and home runs for 10 years in a row.

In four national-level events, playing with three different partners against dozens of elite opponents, Meckstroth finished first, second, third and fifth. He is the only player ever to have won five national titles and 53 regional titles before his 25th birthday. His total of 6,221 master points as of Jan. 10 ranked him 110th in the world -- he should reach 85th place easily before the year is out.

"Pretty clearly, he's the top young player in the country," says Tom Smith, manger of New York's Cavendish Club and a former tournament whiz kid himself.

What makes a championship bridge player?

"Concentration, a will to win, and a desire to win. But mostly it's making sure you never think you know it all," says Meckstroth, a tall, blond, softspoken former schoolboy gold champion. "All bridge players have huge egos, but you have to make sure you're always working to get better."

Meckstroth began his bridge career at 14. His first partner was his father, a credit manager, who taught his son the first rule about bridge: "Never get upset, and never scream at your partner." It took young Meckstroth about one week to learn the basic bidding conversations, and soon the student was better that he teacher. He got better not by studying the theories of the game -- he's read only three bridge books in his life -- but by playing. "I did most of my learning at the table," says Meckstroth. "I've just got the feeling at the table."

He has also refined his game by talking for hours on end about bidding systems with his favorite partner, Eric Rodwell, a Purdue University graduate student. "We actually look forward to those long drives to tournaments because it's time we can use to get better."

Like many top pairs on the international scene, Meckstroth and Rodwell play a highly specialized, artificial bidding system. They use about 200 bids that have precise, coded meanings. Most players use only two systems -- the Stayman convention, which asks a player who has bid one no-trump whether he has four hearts or four spades, and the Blackwood convention, where one player asks his partner how many aces he has.

The use of artificial conventions -- in which bidding a suit has nothing to do with how many cards of that suit a player has -- is becoming ever more commonplace on the international scene, according to Benito Garozzo. "Already, the Poles have their 'Polish Pass,' where they pass with a good hand and bid with a bad one," notes Garozzo. "And the relay systems (where the bidding becomes an entirely artificial series of questions and answers) are here already."

At the 1979 world championship, only the three American pairs and two from Australia played natural bidding systems. Most of the teams used a system in which an opening bid of one club meant "I have some kind of strong hand," and didn't refer to clubs at all.

This year, the U.S. team's toughest competition is expected to come from the Poles, Swedes and French, who defeated the Americans in another tournament, the World Team Olympiad, last fall. "I hate to say this," grumbles Henry Francis, editor of the Contract Bridge Bulletin and a correspndent at the last nine world championships, "but right now any of 11 teams could be better on any given day than a good U.S. team. Things are really evening up."

Ironically, Garozzo and other top European players feel that the United States could diminate world bridge indefinitely if its method of selecting a team were not so democratic. In most countries, teams are appointed for the world championships. The U.S. team is chosen from among the winners of the four major team events each year -- the Vanderbilt, the Reisinger, the Spingold and the Grand National. Those four teams meet in a playoff, and the winner represents the nation.

The other problem the United States has in the world championships is that it can only field four players at a time. In terms of depth, no other country can touch the Americans. As Edgar Kaplan, editor of The Bridge World magazine, put it: "If we played teams of 30, we'd wipe the floor with everybody. But since we only send one team there's no reason to believe that the U.S. will dominate."

And in a few years, it appears, the Americans and European will have someone else to contend with-- the Chinese. Last fall, the most populous nation on earth was admitted to the World Bridge Federation. This month, for the first time, teams from all over the world, including one from Taiwan, will travel to Shanghai for exhibition matches against a Chinese team. By all indications, China is gearing up for a major run at the world championship by the middle of this decade.

Kathie Wir, a naturalized American, the inventor of the Precision bidding system and a former world champion, visited Wu Pie province last year. "I was amazed at the number of people genuinely interested in bridge as well as the grasp of the game shown by their questions," she wrote in a magazine article last fall. "In a few years, they may be our strongest opponents."

There is no such movement in the Soviet Union, however. According to diplomats familiar with Soviet cultural life, bridge is popular only in Lithuania, Latvia and Estonia -- the sectors of the Soviet Union with the strongest European heritage and influence, and thus the strongest bridge tradition. While many bridge officials believe the Soviets are staying out of competition because they know they couldn't win, bulletin editor Francis notes another reason. "Pravda," he says, "still officially maintains that bridge is a game for the upper classes, and thus should be avoided." A $750,000 Deal

The most famous deal in bridge history -- and almost certainly the most expensive -- arose in England sometime in the 19th century. Sitting West was the duke of Cumberland, son of King George III. He fell so in love with his cards that they ended up costing him the modern equivalent of $175,000.

This was the whole hand:

North-South bid a grand slam (declared that they could take all the tricks) in clubs, although history cannot explain why they thought so. They had only an ace and a queen in high cards between the two hands -- and South, who was to play the hand, didn't have a card higher than a 6.

The duke, meanwhile, had the kind of powerhouse that fills bridge players' dreams. However, North-South bragged that the duke wouldn't take a single trick. The duke disagreed -- and backed his judgment by pushing 20,000 pounds into the center of the table.

Of course, the duke fell victim to the astonishingly lucky distribution of the North-South cards -- and to his own fatal opening lead.

He could have beaten the contract and won his bet by leading a spade or a heart, but he opened the seven of clubs. It was won in dummy with the 8. South trumped a diamond and played a club. The duke played the nine, so dummy won with the ten. Then South trumped another diamond, and when the ace and the queen fell, all of dummy's diamonds were now high.

South now played a third club. The duke played the jack, and dummy won with the queen. Now South took away the duke's last trump, the king, with the ace. The lead was in dummy -- which contained nothing but good diamonds.

Bridge historians are almost sure that this hand was predealt dishonestly by the duke's opponents, since the odds of it occurring naturally are more than 63 million to one.

But historians say the duke was an inveterate enough gambler to bet against his opponents even if he suspected them of rigging the hand. Like most gamblers, he got an education. Tricks to Remember

So you want to become more of a killer at the bridge table? It may not only be a question of bidding and playing technique. Here are some hints about "table presence" from some of the country's top professionals:

Don't play too fast. More bridge hands go down in flames because of careless haste than for any other reason. Care preprogrammed pauses into your rhythm at the bridge table. When playing a hand, force yourself to stop and think once the dummy comes down -- even if there doesn't seem to be much to think about. When defending, take time during trick nine to think about what you'll do during trick 12.

Keep resorting your cards throughout the hand. An alert opponent will notice where you were holding that six of diamonds you just played. If you've pulled it from the far right side of your hand, and you're not a "resorter," it's likely that the six was your lowest diamond.

Avoid telltale grimaces and "huddles," especially before making the opening lead. Opening leads make or break more contracts than any other play, bid or brillance. If you fidget, glower and groan before your opening leads, an alert opponent will figure out what your problem was. Because of clues from the bidding, an opening lead is almost never a complete stab. If it often seems that way to you, think about your opening lead during the bidding -- not just after it.

Develop a ritualized method of remembering the cards that have been played. The most popular expert technique is to "read" each trick to yourself silently as it's being played. Don't just remember that the guy on your right won it with the king. "Say" to yourself: "Three of clubs, four, jack, king," as they're being played.

Hold your cards close to your chest. If you show your hand to an opponent, it is not only legal to look, but human nature makes it almost inevitable.

Most important: Always sound and appear confident. Experts say they often will decide whether to make an aggressive play or a passive one on the basis of how nervous their opponents look. If your opponents consistently do the right thing in bridge's "iffy" situations, the reason may be your furrowed brow, or that resigned-sounding five-spade bid you just made.