The Houston Rockets have a new slogan these days: "Yes, we can." The fact that the slogan is 5 years old and completely unoriginal bothers no one.

"Remember," Rocket Coach Del Harris said, "this is all new around here. This isn't Philadelphia, you know."

Sunday, as the Rockets were finishing their 100-89 victory over the Kansas City Kings to take a 3-1 lead in the NBA Western Conference final series, one of the "Yes, We Can," signs given to Houston fans cascaded onto the court.

Furious, Kansas City Coach Cotton Fitzsimmons raced onto the court and grabbed official Lee Jones, screaming at him to stop play.

"I didn't want someone tripping on the sign and getting hurt, tearing up a knee or something," Fitzsimmons said later. "These fans don't understand basketball. There's a thing called class that comes with knowing the game. They have it in Portland, New York, Philadelphia. These fans are like our fans in Kansas City. They don't know the game yet."

Fitzsimmons' words make a significant point about this series, which resumes here Wednesday night. In the east, the conference final is between two teams and two cities that have great, longtime basketball traditions. The Philadelphia-Boston rivalry has a niche in basketball history regardless of what happens this week.

In Kansas City and Houston, there is no tradition. There are no memories, no longtime rivalries. Houston has had pro basketball since 1972, when the Rockets moved there from San Diego. Only once before, in 1977, have the Rockets advanced this far in the playoffs.

Kansas City has had the Kings for seven years, the team moving here from Cincinnati in 1974. This is the Kings' first time in the conference finals.

"We have 7,200 hard-core, loyal fans in Kansas City," said Fitzsimmons, coach of the Kings for three seasons. "We're still trying to educate the fans in this town. We're hoping these playoffs will create more fans for the future."

Less than a year ago, it looked as if pro basketball's future in Kansas City might be extremely limited. After a partial collapse of the Kemper Arena's roof in June, the Kings were no longer obligated to remain here under the terms of their lease.

With attendance hovering around 7,000, there was talk of moving the club to Minneapolis. The city government, which had already seen the hockey team for whom the arena was built shift to Denver, put together an open-ended sweetheart lease for the Kings. Still, before the Kings' late-season playoff drive, there were murmurings that the team might be moved."

That talk has now been stilled, even though the Kings have yet to play before a sellout crowd in the playoffs. The first two games of this series drew 13,000 and 14,000 to the 16,800-seat arena. The Kings had one sellout during the regular season -- for a game with the 76ers.

"People came to see the Doc (Julius Erving)," Fitzsimmons said. "I'd be crazy to think different."

In Houston, the situation is better because the Rockets have been a fairly solid club in the five seasons since Moses Malone arrived there, making the playoffs four times.

All six of the Rocket playoff games have been sold out (16,121) but each time the last tickets went on game day and only after it was announced that there would be no local TV. During the regular season, the Rockets averaged 9.500 fans per game.

Calvin Murphy, who has been with Houston since it moved here in 1972, is aware of that.

"It's come a long way," he said. "When we got here, no one in Houston knew beans about the Nba or cared. We played in privacy. Now, if we do well, at least people notice. We still can't compete with football but the difference is like night and day. Now, when we have a big game, the place rocks. That's progress."

"The bottom line, though, is tradition," said the Kings' Sam Lacey.

"When a team is established for years in one town, then fans become their fans, win or lose. When a team is new, lacks that tradition, it needs to win to create interest and to create a tradition."

A prime example of the Lacey theory can be found in New York. There, the football Giants have not won for 18 years.They still sell out 76,000-seat Giants Stadium in the New Jersey Meadowlands each home game.

The Jets have not won for 10 years. They have trouble selling out 55,000-seat Shea Stadium. The Giants have been in the New York area 30 years longer than the Jets. Tradition

Houston and Kansas City were expected to make only brief appearances in these playoffs, each ending the regular season with a 40-42 record. But each pulled two stunning series upsets, thus creating new fans, new interest and generating excitement in their towns.

Yet the sign at the Kansas City airport reads: "Welcome to Kansas City, home of the Royals and Chiefs." The biggest round of applause at Houston's Summit Sunday came when Earl Campbell took a front-row seat.

But for these two cities, it is a beginning. "Each time our fans see a good game, they learn, they become more involved and they're more likely to come back next year," Harris said. "It isn't as if you make a place a basketball city overnight. It takes a while."

In short, it takes, as the late Zero Mostel used to sing: "Tradition!"