The profits of Playboy magazine are slipping because of "soft newsstand sales," and executives of Playboy Enterprises Inc. said yesterday there is cause for "concern" about efforts to pressure stores to stop selling the magazine.

The company reported a $3.2 million loss for its third quarter, which ended March 31, but blamed most of the red ink on a failed attempt to revive its once-popular Playboy Club empire. The last Playboy-owned clubs will be closed, leaving only three franchised Playboy clubs in Omaha, Des Moines and Lansing, Mich., the company said.

The campaign by conservative religious groups to halt sales of Playboy and other sexually explicit magazines gained momentum yesterday when Thrifty Corp. of Los Angeles announced it would stop selling Playboy and rivals Playgirl and Penthouse at its 582 drugstores.

Last month, Southland Corp. announced that it would cease selling Playboy and Penthouse at the 4,500 7-Eleven stores that it owns and operates because of pressure from such groups. A large number of 7-Elevens are franchised and not operated by Southland. People's Drug Stores, which is based in Alexandria,also has discontinued selling magazines such as Playboy.

Playboy's president and chief executive, Christie Hefner, said that, although Playboy magazine has lost outlets, it has not lost "purchasers, and we expect that our readers will continue to buy their Playboy magazines in other stores."

Hefner, the daughter of Playboy founder Hugh Hefner, said, "Sadly, a small group of ultraconservatives who want to control what all adults read and see have created an atmosphere of confusion in which legitimate concerns about violence and child abuse somehow spill over to a responsible publisher like Playboy. We hope that the true majority will recognize the dangers of this and make their views known."

Playboy spokeswoman Robyn Radomski said that the loss of 7-Eleven and other outlets has not had a material impact on Playboy newstand sales and said that more than 60 percent of the magazine's 4.1 million monthly circulation is by subscription. The 7-Eleven stores represent 5 percent of Playboys nationwide outlets, but Radomski said she did not know what percentage of newsstand sales the stores represented.

Overall, Playboy reported third-quarter revenue of $42.8 million, down from $45 million a year ago. In that period, it lost $346,000 compared with the $3.2 million loss reported for the most recent quarter.

For the first nine months of its fiscal year, Playboy reported a loss of $36.8 million compared with a profit of $7.5 million for the first nine months of fiscal 1985.