WHFS, the feisty little radio station whose progressive rock format had been endangered by its sale last December, apparently has been saved, or at least its format has.

Recently sold to the Outlet Co. for $2.1 million, WHFS won a reprieve yesterday when a new company, formed by a group of officials connected with WHFS, signed an agreement to purchase WEAM for $1 million in cash. The agreement includes a 30-year lease on 11 acres of land and broadcast facilities in Falls Church. Papers are expected to be filed with the Federal Communications Commission Monday.

The new company, Cardinal Broadcasting Associates, which will retain ownership of the WHFS call letters, announced it will transform WEAM, once a top-rated Washington station, to AM stereo. WEAM's 5000 watts of power will almost double the exposure area of WHFS' 2400 watts.

Earlier this week, Outlet, a Rhode Island broadcasting conglomerate that owns WTOP-AM, was purchased by the Rockefeller Center Inc. for $322 million. Although Outlet's purchase of WHFS has not yet been approved by the FCC, it was included in the RCI purchase, which also is subject to FCC approval. A spokesman for Cardinal said he expected the deal with WEAM to be completed within 60 to 90 days.

Major partners in the new company are Phillip Margolius, former president of WHFS, and Jake Einstein, executive vice president at WHFS. David Einstein, the station's highly regarded program director, will be president of the new company. "The entire staff of disc jockeys and most of our employes will go to WEAM," said Jake Einstein.

One of the points negotiated with Outlet, which plans to turn WHFS into an FM adjunct to WTOP's news programming, was that the old owners retain the station's tremendous record library. "We own that music and it's going with us," Einstein said yesterday. David Einstein added that "we expect to continue the progressive sound, exploring new music and giving as much exposure as possible to local bands."

WEAM--which was the first full-time rock station in Washington--went on the air in 1947 and was purchased in 1948 by the Thoms family of Raleigh, N.C., which has owned it ever since. In the era of the WEAM Team, the Lively Ones and the Red Coats (as the station's deejays were known) it was one of the most popular stations in the metropolitan area, often ranked number one.

The '70s proliferation of FM and FM stereo broadcasting took away much of AM rock radio's thunder and WEAM's ratings had been slowly sinking in recent years. It experimented with several formats, ranging from rhythm and blues (it became the first suburban soul station) to progressive rock to its current big band sound. In one 18-month period, the station went through two general managers, three program directors, two music directors and nine announcers.

"WEAM was the top station in town for many years," said Jake Einstein, "and we expect to bring it back to that."