The Dallas Cowboys, dubbed "America's Team" by some high-flying public relations folks, have slipped a peg or two in popularity, according to one benchmark -- the sales of posters, penants, underwear, T-shirts and other professional football paraphernalia.

For years, the Cowboys dominated the sales of souvenirs by NFL Properties, the league's marketing agency. They won more games than any other NFL team in the 1970s. Their cheerleaders were the leggiest, their television ratings highest, and their souvenir sales biggest.

(The teams don't share the $225 million in souvenir sales, says John Bello, vice president for marketing of NFL Properties. Manufacturers get most of the proceeds, and the rest goes to selected charities.)

In 1979, nearly 27 percent of the souvenirs sold through NFL Properties had the Cowboy emblem. The Pittsburgh Steelers were next, with 20 percent of the sales.

"The Redskins weren't all that bad," Bello said.But not great, either. Washington ranked 10th, with 2.9 percent of the sales, trailing the Los Angeles Rams (4.3 percent), for instance, but finishing well ahead of the Detroit Lions (1.4 percent) and San Francisco 49ers (0.7).

This year, however, the Cowboys are trailing both Pittsburgh and the Houston Oilers, Bello said. They aren't likely to catch up without Roger Staubach.