A year ago, when Dianne Fromholtz came to Washington for the first tournament of the winter women's protennis tour and started rushing the net, her colleagues gasped. The talented Australian left-hander had always preferred to play from the backcourt, treating the forecourt as it were booby-trapped territory.

Now she is comfortable with her more aggressive, all-court style, trim and fit after some intensive conditioning back home. Last evening, she defeated Pam Teeguarden, 6-2, 6-2, to reach the semifinals of the $125,000 Avon Championships at George Washington University's Smith Center.

Moving exceptionally well and taking the net at every opportunity, Fromholtz won a match that was more competitive than the scores make it seem. It lasted 90 minutes, and four games went to deuce at least three times.

Fromholtz held her serve after five deuces and four break points in the second game of the first set. She broke Teeguarden after seven deuces and seven break points in the first game of the second set.

Fromholtz -- who beat Australian Federation Cup teammates Wendy Turnbull and Kerry Reid in the finals of two tournaments in Sydney last month -- has largely tamed an erratic forehand. She always had a big, intimidating topspin backhand.

But her biggest improvement has come on the volley. Her net game is still somewhat erratic, but now a formidable weapon.

"I've been working on it for a year. It's now part of may game... Before I used to kind of jab at it, but now I hit it harder and get more pace," Fromholtz said.

"I'm still not a net-rusher. I have a solid baseline game. But I think it's important to have both. It takes a long time to change a backcourt game to a net game and put it all together, but I have settled down quite a bit now. "I'm very confident. And I've always trained very hard."

Fromhotz has climbed back into the top 10 in the computerized rankings of the Women's Tennis Associaion after having an off-year in 1977. In the space of six months she was sidelined with mumps, measles, chicken pox, influenza, and an allergic reaction to a vitamin B-12 injection. It was a nightmare, like having all the ills of childhood on top of one another.

Fromholtz chose to concentrate on tennis instead of ballet at age 10. At 16 she went to England and first made an impact on the international circuit, winning several small tournaments while traveling with her mother and living in a camper.

She is one of the few contemporary players who have beaten Chris Evert -- she has done it twice -- and she thinks she is ready to have a big year. Fromholtz lost her serve twice -- after grabbing a 3-0 lead in the first, set, and breaking in the first game of the second -- but kept Teeguarden, a tall, thin Californian, under constant pressure. She took advantage of Teeguarden's weak second serves, either blasting deep returns or chipping down-the-line and darting swiftly to the net.

In today's afternoon semifinal starting at 2, Fromholtz will play Wimbledon champion Martina Navratilova, the top seed who has won the Washington tournament three of the last four years.

Navratilova served erratically, but dominated the net, in an uninspring 6-3, 6-1, victory over Ann Kiyomura of San Mateo, Calif., last night.

Navratilova lost her serve once, in the fourth game of the first set, in whcih she did not get a first serve in. But Kiyomura was too timid in her light-hitting, backcourt style to put any substantial pressure on Navratilova's unrelenting attacking game.

Navratilova has been suffering from a heavy cold, but she timed her volleys much better than she had in her-second-round victory over Ruta Gerulaitis Thursday. CAPTION:

%picture, Dianne Fromholtz returns a shot to Pam Teeguarden. By Richard Darcey -- The Washington Post