Second-seeded Pam Shriver advanced to the semifinals of the Virginia Slims of Washington tennis tournament by defeating seventh-seeded Bonnie Gadusek, 7-6 (11-9), 7-6 (7-3), last night at George Washington University's Smith Center in front of 4,900 fans, including Vice President George Bush.

Shriver next plays fourth-seeded Manuela Maleeva, who advanced to the semifinals with a 6-3, 6-4 victory over sixth-seeded Helena Sukova.

Kathy Rinaldi became the only seeded player to be eliminated before the quarterfinal round as unseeded Bettina Bunge defeated eighth-seeded Rinaldi, 3-6, 6-4, 6-3, in a second-round match.

Bunge, who, prior to Wednesday, hadn't won a match since early August, will play fellow West German Claudia Kohde-Kilsch in a quarterfinals match today.

Rinaldi appeared headed to her first win over Bunge, after winning the first set. But Bunge came back in the second set despite holding her serve just twice -- because Rinaldi held just once.

"I didn't start out all that well, and I just tried to hang in there," Bunge said. "I'm just glad I didn't give up even if things didn't look good."

As for the wackiness of the second set in particular and the match in general, Bunge said, "For me, it's pretty typical."

Bunge attributed her lack of success in the latter part of 1985 to a lack of confidence.

"The skill shots tend to go and you lose confidence," she said. "I'll hit some unbelievable shots and then miss some easy ones . . . . I didn't play enough matches and I didn't win enough and the confidence goes."

Bunge was ranked sixth in 1983, but is now 23. Kohde-Kilsch, on the other hand, has moved up to No. 5. Bunge beat Kohde-Kilsch in their last meeting, the quarterfinals of the German Open in May.

Since then, Bunge said, "She's been very consistent, while I haven't been consistent at all."

Sukova, seeded sixth here and ranked ninth in the world, likes to serve and volley. But Maleeva, seeded fourth and ranked seventh, kept her at the baseline by hitting deep, making her passing shots and putting the ball at Sukova's feet when the 6-foot-1 1/2 Czech did venture to the net.

"This is what I'm supposed to do against someone who has good volleys and likes to play at the net," Maleeva said. "I tried to keep her from the net and make her play at the baseline. I'm more consistent on baseline than her.

"It was pretty good, but not like I want it," she said. "I was making some mistakes I usually don't do. Mistakes from the baseline on balls that weren't hit that hard, and I missed a few easy approach shots on my forehand."

The two had played in the semifinals of a tournament in Tokyo in the second week of December. Because she won that match, 6-0, 6-2, Maleeva said she expected Sukova to stay at the baseline a bit more this time.

"In that last match, I hit some great passing shots," Maleeva said, "so that's why she had to stay at the baseline more."

Said Sukova, "I played just horribly in Tokyo. But when you come to the net, you need to come after a good approach shot. If you come any time, it's too easy to pass, and she has good passing shots."

Sukova broke Maleeva in the first game and was serving at 30-40 in the second game, when Maleeva hit a passing shot, cross court, to break Sukova.

Both players held serve until the eighth game. With Sukova serving, Maleeva hit three straight forehands for winners, and won the game as a Sukova forehand sailed wide. Maleeva then held serve to win the set, 6-3.

The beginning of the end for Sukova was the first game of the second set when Maleeva broke her serve. Maleeva made it 2-0 with an ace and a backhand down the line.

In the fifth game, Maleeva started by ripping a backhand return for a winner. She was at break point after hitting a forehand at Sukova's feet that Sukova could do nothing of value with. Maleeva then broke with a forehand cross-court volley into the open court.

Sukova made things a bit close by breaking Maleeva in the sixth game and then holding serve, to make it 4-3. But Maleeva held from then on.

"Sure, I was disappointed," Sukova said. "Today, I had chances . . . . I always had opportunities. If I make some of those points, it could go the other way."

Maleeva will be 19 on Valentine's Day, and is at a point in her career when she wants to expand her game forward, as in away from the baseline.

"I've improved my serve and volley, and I would like to go to the net more," she said. "I have a good volley and I'm not afraid to hit a volley. I have to work on my approach shots to go to the net."

There is no daytime session today because the George Washington men's basketball team will be playing St. Joseph's. The evening session will begin at 7:30. TODAY'S SCHEDULE Evening Session (7:30)

Martina Navratilova (1) vs. Zina Garrison (5); Claudia Kohde-Kilsch (3) vs. Bettina Bunge; Betsy Nagelsen-Barbara Potter vs. Mary Lou Piatek-Anne White.