WASHINGTON (AP) _ A group of friends has purchased a $2.5 million California estate for President Reagan and his wife, Nancy, but the first couple may decide against living there when the president's term ends, says a spokeswoman.

Cable News Network, citing White House and West Coast sources, reported today that about 20 friends of the Reagans set up Wall Management Services and purchased the 1 1/4 -acre estate in the exclusive Bel Aire section of Los Angeles on Aug. 21, 1986.

The estate includes a secluded house with 6,500 feet of living space and a pool. The house was purchased from a 90-year-old woman who still lives there and is leasing the property back, the network said.

The friends put up the money with the understanding that the Reagans, whose money is in a blind trust, will pay it back, the network said.

But Elaine Crispen, a spokeswoman for Mrs. Reagan, said ''the Reagans themselves have not yet bought a home,'' and may choose to purchase another house.

''It could be one that the Reagans may buy when the time comes, but they're still looking at others,'' Ms. Crispen said Friday. ''They've always said that their home after Washington would be back in southern California.''

Reagan's term ends in January 1989.

Ira Revich, an attorney, acted as an agent for Wall Management Services, which was set up for the sole purpose of purchasing the estate, the network said.

Friends of the couple said the Reagans think their ranch in the hills near Santa Barbara is too small and too isolated for the first lady, according to the network.