Nancy Conz, a 24-year-old from Easthampton, Mass., charged ahead at the start and stayed ahead the rest of the way for an easy victory in yesterday's Avon women's 20-kilometer race at Hains Point.

Conz's time of 1:09.30.5 was only 3 1/2 seconds short of the American women's 20-kilometer record, and she might well have broken the mark had it not been for a wrong turn taken by the lead car at Buckeye Drive and Ohio Drive SW on the first of the race's four laps around East Potomac Park.

As Conz followed the car onto the wrong roadway, several race monitors shouted at her, and she stopped briefly before being directed to the proper route.

"It was kind of frustrating because I didn't know which way to go, but I don't think it would be fair to say that's why I didn't get the record," said Conz, who won the Avon International Women's Marathon last summer in Ottawa.

Finishing second yesterday, almost a full three minutes behind Conz, was Eleanor Simonsick, 23, of Washington in 1:12.27.9.

Marge Rosasco, 33, of Fallston, Md., who finished third in the Avon race here last year, was third again, in 1:12.57.8. All three will receive expense-paid trips to this year's Avon marathon in San Francisco in June.

More than 600 runners had registered for the race, but only 406 finished on a cold and blustery day.

Possibly the loudest cheers from the sparse group of spectators came for Ruth Rothfarb, an 80-year-old widow from Miami, who last summer became the oldest woman ever to complete a marathon, at the Avon International in Ottawa.

Rothfarb finished in 2:26.33, but appeared very tired and had to be helped to a medical tent where she was examined by Dr. David Brody, a sports medicine specialist. "She's fine," Brody said later. "She's a great lady."

Said Rothfarb, "I haven't been training lately. But I never worry about the time. As long as I finish, I'm happy. I feel fine now."

Conz ran the first mile of the race in 5:29 and stayed close to that pace throughout. Her time at the five-mile mark was 27:39 and, at 10 kilometers, the halfway point, it was 34:18.

For about the first half of the race, eight runners were bunched, vying for second place behind Conz. But at the 10-kilometer mark, Rosasco said she turned to Simonsick and suggested they pick up the pace.

"I couldn't see 10 people all coming in second," said Rosasco.

Rosasco and Simonsick and two other runners, Sue Crowe and Jane Welzel, pulled ahead at that point, but after about two more miles, Crowe and Welzel fell behind and Simonsick pulled ahead of Rosasco.