With retro fashions hot, New Balance Athletic Shoe Inc. is relaunching the PF Flyers brand with a line of casual footwear stylish enough to be sold at a Newbury Street boutique.

Shoes for fashionable Newbury Street are a first for a Boston company best known for no-nonsense performance sneakers, a favorite choice of middle-age runners who take their 5-mile jogs seriously.

By using PF Flyers as a subbrand, the company hopes to get into the fashion business and pursue some younger customers in new retail venues without the risk of diluting New Balance’s reputation as a performance brand.

According to Paul Heffernan, executive vice president of global marketing, New Balance wrestled with the idea of getting into the fashion arena two years ago after it bought the rights to PF Flyers, a brand that had been dormant for about a decade.

“We asked ourselves, `Is this something we want to do? ” said Heffernan, who added that other strategies were considered for using the PF Flyers name.

Fashion has always been important for athletic footwear giants such as Nike Inc. and Reebok International Ltd. of Canton. Both companies have seen their classic styles, modeled on sneakers popular years ago, regain favor.

“If youre a top [athletic footwear] brand, you need to have both performance and fashion,” said Bob McGee, editor of the trade publication Sporting Goods Intelligence.

Many companies sell performance and fashion shoes under the same brand name. But New Balance is taking a different approach. To avoid confusing consumers, it will continue to sell performance sneakers that generally cost $70 and up in specialty running stores under the New Balance name; it will use PF Flyers to sell an “active casual” line to a younger boutique shopper with a price range of $40 and up.

As a private company, New Balance can grow the PF Flyers brand patiently, Heffernan said. If all goes well, PF Flyers could ultimately generate “$100 million plus” in annual sales, he said. But if PF Flyers “doesnt gain traction in the boutiques” and win space in more stores, it may end up as a niche brand, he said. New Balance had 2002 sales of $1.3 billion, up 14 percent, the company said.

PF Flyers were originally launched in 1937 by B.F. Goodrich. This year’s spring styles update the brand’s “comfort” heritage, said Lisa Bida, the line’s senior product manager.

“The PF in PF Flyers stands for Posture Foundation,” she noted.

As for taking pains to keep the New Balance and PF Flyers brands distinct, Heffernan said, “We dont want New Balance to be all things to all people.”