Something important happened last night in the D.C. National Bank Tennis Classic. Yannick Noah, the man who was partly responsible, played it down, talking softly, as he usually does.

Noah defeated Hans Gildemeister, 6-4, 3-6, 6-3, and earlier Rodney Harmon of Richmond beat sixth-seeded Raul Ramirez, 6-3, 7-5. According to Dewey Blanton, a spokesman for the Volvo Grand Prix, never before have two black players qualified for the quarterfinals of a Grand Prix event. The Grand Prix was begun in 1970.

Noah, who is always soft-spoken, said quietly, "It's good, it's good for him. There are not many blacks on the tour. He's going to answer some of the questions for a change."

Then he smiled, "I hope he gets to the semis."

The development is not really surprising in light of the performance of young black players like Chip Hooper, Lloyd Bourne, Zina Garrison and Leslie Allen. "It's nice to have some blacks," Noah said. "For me, it is no change (to get to the quarterfinals). It doesn't make a difference. He's American. I hope he's proud for himself."

Joining them in the quarterfinals, as expected, are Ivan Lendl, and Jose-Luis Clerc, the first and second seeds. Lendl won with ease, beating Jose-Luis Damiani, 6-3, 6-1; Clerc struggled before beating Jiri Granat, 5-7, 6-2, 6-1.

In the first set, Clerc did not appear to be the world's best clay-court player: Granat did, breaking Clerc in the last game. But, Clerc, who was not available for comment later because of new problems with his right Achilles' tendon, broke back from 15-40 in the first game of the second set, just to show who's who, when Granat netted a backhand volley. After that, the match was his.

Also advancing to the quarterfinals were Eric Fromm, who defeated Jaime Fillol, 6-0, 6-4; Van Winitsky, who beat eighth-seeded Mel Purcell, 6-3, 6-1; Bernard Fritz, a 6-4, 6-7 (7-1), 6-4 winner over Pablo Arraya, and Jimmy Arias, who defeated Claudio Panatta, 7-6 (7-3), 3-6, 6-1. Today, Noah plays Winitsky, Fritz faces Clerc, Lendl plays Harmon and Arias--at 17 America's answer to Mats Wilander--faces Fromm.

At 3-3 in the first-set tie breaker, Arias hit a backhand winner that gave him back an edge along with the serve. On the next point, Panatta, another clay-court specialist, hit a lob that most people would not have gotten to. But Arias is not like most people. He got to it--and Panatta--by hitting a backhand winner off the lob. Arias then served an ace on the next point.

"In the first set, there was a lot of tension and a lot of running around," Arias said. "In the second set, he did most of the running even though he won. So in the third set, he was a half step slower and that made the difference. That's what helped me break his serve twice."

If it was a day for history and youth (Harmon and Arias), it was also a day for anarchy. All week players have been grumbling, mostly under their breath, on court about line calls. Yesterday, Lendl and Damiani staged a bit of an insurrection.

Lendl was leading by a set, and 2-0 in the second. He served deep to Damiani's forehand. The chair umpire, Phil Adams, called it an ace. The players, together, disagreed. Lendl served again to the same court. Damiani quickly lost the point, anyway, but the players had made theirs.

"If he's wrong, and we know each other well and we agree, it is stupid to listen," Lendl said. "Even if he is supposed to be the arbitrator, we both agreed it was out. We'll tell them what the score is afterward."

The unhappiness with the umpiring did not end with that match. Both Noah and Gildemeister complained. "The whole week there have been really bad calls against me and in favor of me," Gildemeister said. "You lose concentration because you don't have faith in the linesmen."

Once, after a ball went obviously wide, Noah called out in the mock emphatic tones usually reserved for officials, "Out!!!" The most crucial point, both agreed, came not on a bad call, but simply on a bad ball by Gildemeister. It was 2-2. Gildemeister had earned a break point but squandered it. With the court wide-open to him, he hit his two-fisted forehand wide and it was deuce.

Noah held on to win the game, and broke in the next when Gildemeister's drop shot that landed just wide was called out, just as he got to it. Once, again, at 5-3, serving for the match, Noah faced a break point and faced it down. "I was very lucky to win that one," he said. "It was very close."

A close call, one might say.