When Carroll Dawson, the general manager of the Houston Rockets, met Yao Ming two years ago, one of the first questions he asked him was, ”Why don’t you dunk the ball?”

”He told me he had been taught not to embarrass his opponents,” Dawson said yesterday, recalling the conversation. ”I said, ‘Well, that’s something that’s going to have to change, because if you don’t dunk in our league, 6-foot-6 guys will block your shot.’ Yao said, ‘I’m ready for the change.’ ”

Yao, the Rockets’ 7-6 center from China, has kept his word, dunking regularly while establishing himself as a force and an N.B.A. All-Star for years to come.

But Yao, who will make his first appearance of the season at Madison Square Garden tonight when the Rockets (19-15) and their coach, Jeff Van Gundy, visit the Knicks (14-22), has yet to develop the aggression and the ferocity that the game’s most powerful play, the slam dunk, has come to symbolize.

Many observers believe his ability to do so will determine whether he becomes an all-time great center, which was part of the expectation when the Rockets made him the first pick of the 2002 draft, or just a very good player in his era.

”If he ever gets a mean streak in him, look out,” said an Eastern Conference official who spoke on condition of anonymity. ”But his culture and his background might not allow that. If he can get that, wow! If he gets that mean streak, he’s fighting Shaq in there.”

Though Yao has had some of his stronger performances against Shaquille O’Neal, the Lakers’ center, he is nowhere near the dominant force that O’Neal is or was during a similar stage in his career. Yao entered last night’s game at Detroit with solid but not standout averages: 15.9 points, 9.0 rebounds and 1.88 blocks.

With his size, soft hands, great passing ability and varied arsenal of shots, Yao could do much more. And while Van Gundy and his assistants understand that Yao, 23, is still a work in progress, they are sometimes frustrated by his tender nature on the court.

One of Patrick Ewing’s main responsibilities as a Rockets assistant coach is to work with Yao, and Van Gundy referred all questions about Yao’s development to Ewing.

”He just needs to become more aggressive,” said Ewing, who is in his first season with Houston. ”Right now, he’s too gentle. He’s like a gentle giant. He’s got to be more physical and aggressive. Instead of waiting, he needs to just take it. Show his dominance. Use his size, and just take it.”

Though Yao needs to incorporate that mentality at both ends of the floor, the Rockets have mainly focused on his view toward offense. Instead of settling for a fadeaway jumper, they want him to pound the ball toward the basket for a layup or a dunk. Instead of submitting meekly to double teams, in which defenders have been getting incredibly physical with Yao, they want him to throw an elbow that will discourage opponents from going at him so hard.

And despite Van Gundy’s desire to feature him more, Yao, a 51 percent shooter, is averaging only 11 shots a game.

Part of that is because of Houston’s shoot-first guards, Steve Francis (15 shots a game) and Cuttino Mobley (13), but Yao must also be more demanding for the ball.

”I haven’t reached Coach’s expectations yet,” Yao, through his interpreter Colin Pine, said in a telephone interview Tuesday. ”I just have to keep working at being more aggressive and being nastier.”

But Yao is somewhat confused. Asked how to go about doing that, he said: ”I don’t know. If I knew the answer to that, I think I would’ve already met Coach’s expectations.”

Donnie Nelson, the Dallas Mavericks’ president of basketball operations and an expert on international basketball, said Yao was being asked to embrace an entirely different way of thinking from what he is accustomed to.

”If you think of how community-oriented most young people growing up in China are, it’s just a different way of being brought up,” Nelson, who has been to China several times, said. ”There’s a lot more unity, and it seems like it’s a culture that promotes a more unselfish, ‘what’s best for everyone is what’s best for you’ mentality.

”In our culture, it’s almost exactly the opposite. To achieve the American dream, you’ve got to outhustle, outfight, out-think, outeverything your competition. So it’s a completely different political/socioeconomic background than we’re raised in. I don’t know how much that has to play in his approach, but I think that it is somewhat of a factor because in a lot of the team sports in China, you don’t see the same kind of one-on-one domination. It’s more team-orientated, whereas over here, it’s ‘I’m going to torch my guy, then only when the double team collapses will I look to make the pass.’ ”

The agent Bill Duffy, a member of Yao’s management team, said Yao was raised not to place himself above anyone else, even on the basketball court. Thus, Duffy and the Rockets have stressed to Yao that taking over on the court does not mean he is being selfish.

”We talk to him and we use Tim Duncan as an example,” Duffy said. ”He’s a nice, gentle person, but every minute he’s on the floor, he’s productive and active. Yao needs to pick up that disposition. It will come with time, when he realizes that by being more dominant he is helping the team.”

Yao acknowledged that his culture played a part in his difficult adjustment.

”There are cultural reasons,” Yao said. ”But I don’t want to use that as an excuse because basketball is an independent culture.”

Yao’s limited exposure to American basketball is also a factor in his approach to the game.

”International basketball is a noncontact sport,” Dawson said. ”We play a more physical, rougher game over here. The N.B.A. is a combination of rugby and basketball put together. So Yao’s got to find out what’s legal and what’s illegal. He’s got to learn how to be aggressive within the rules.”

Yao has tried to be more aggressive lately, but it has backfired and gotten him into early foul trouble.

As a result, his minutes and production have dropped significantly. After averaging 17.2 points, 10 rebounds and 35 minutes over the first 20 games, he has averaged 13.8 points, 7.5 rebounds and 30 minutes over his last 13.

”It’s not just about being more aggressive and being meaner out there on the court,” Yao said. ”You have to be able to temper that with being smart. When I try to go out and just be more aggressive, the result is not too good. Now, I have to find a way to balance the two out — be aggressive and maintain my basketball smarts.”

Yao’s ability to find that balance could be the difference between a career that is immortal and one that is merely exceptional, between championships for the Rockets and mere playoff appearances.

”He’s All-Star caliber, but going beyond that is where personality takes over,” Portland General Manager John Nash said. ”Does he want to be or does he have the determination to be Hakeem Olajuwon or Patrick Ewing? I don’t know. Certainly, he’s good enough to win with. Is he good enough to win championships with? We’ll see. He’s got the physical tools and the talent to be as dominant as any player in the game. He can be as dominating or as successful as he wants to be.”

Photos: Thomas Bello, 3, cheered Yao Ming at a game in Houston. Yao has solid numbers but is still a work in progress. (Photographs by Associated Press)(pg. D1); Center Yao Ming charging into an opponent. The Rockets want Yao to be more aggressive. (Photo by Associated Press)(pg. D6)