NEW YORK — If there was a retailing rookie-of-the-year award, Speedo Authentic Fitness would win by a landslide. Since its November opening, sales at the Authentic Fitness Corp.’s flagship store on Park Avenue here — and its seven other units — are running 15 percent ahead of expectations. Overall volume in fiscal 1994 is projected at $39 million.

“The stores beat expectations in terms of sales and units. It’s a very exciting concept,” said Linda J. Wachner, chairman and chief executive officer. The first Speedo Authentic Fitness outlet opened at the Beverly Center in Beverly Hills, Calif., in November 1992, then was followed by Garden City, N.Y.; Seattle; Scottsdale, Ariz.; Boston, and Paramus and Woodbridge, N.J., locations. Units in Denver and Costa Mesa, Calif., will make their debuts next month, with a total of 40 new stores planned for 1994.

The stores are the retail cornerstone of the fast-growing publicly held company, which announced a 2-for-1 split on common shares January 10. The stock has doubled — going from $14 to $28 — in the past 18 months.

Figures for the retail division were not available, but net revenues for the entire company increased 31 percent to $132.9 million in the fiscal year ending July 3, 1993, up from $101.5 million the prior year. Profits for the same period were $47.4 million, up 23.4 percent from $38.4 million in 1993. In addition, in the first quarter of fiscal 1994, net revenues increased 19.7 percent, to $28.6 million from $23.9 million. Profits were up 13.9 percent, to $9.8 million from $8.6 million.

The 1,100-square-foot store at 39th Street and Park Avenue here features a product mix of 65 percent fitness apparel and 35 percent swimwear. Assistant manager Kimberly Tieng reported that it sold a “surprising amount” of swimwear during the holidays. “A customer would come in and buy three suits,” she noted.

Bestsellers in women’s apparel at the New York store include bra tops at $24, leggings at $33 and biker shorts at $29, all in cotton and Lycra spandex, as well as fully lined racing swimsuits of Antron nylon and Lycra with a zip-down back at $65. Items such as unhooded fleece jackets at $40 and hooded versions at $50, microfiber pants at $40 and Tactel nylon and spandex leggings at $35 are selling well in both men’s and women’s.