Like couples everywhere who see retirement on the horizon, Nancy Reagan is letting it be known that she is thinking about where she and President Reagan will live when he leaves office 3 1/2 years from now.

The first lady talked about her house-hunting plans to Elizabeth Taylor Tuesday night at the state dinner for Chinese President Li Xiannian. Friends say the Reagans want to return to California when the president's term is ended and that they are especially fond of the Pacific Palisades area of Los Angeles, where they once lived.

"I'm not aware that she is actively looking for a house, but I'm sure it's a concern," Mary Jane Wick, Mrs. Reagan's longtime friend, said yesterday of a United Press International report by Helen Thomas that the first lady is quietly passing the word among friends.

"It's not a preoccupation at the moment," UPI quoted one Reagan friend.

The news met predictably favorable reaction in Pacific Palisades.

"I've got just the house for them," Joyce Abbott, manager of the new Pacific Palisades office of Coldwell Banker, said yesterday.

Coldwell Banker's Brentwood office handled the 1982 sale of the five-bedroom Pacific Palisades home that the Reagans sold for more than $1 million. Since then, on trips to California, the Reagans have stayed at their 688-acre ranch near Santa Barbara or at a Los Angeles hotel.

The Reagans' other house was a 4,762-square-foot contemporary ranch-style in the Riviera section of Pacific Palisades overlooking the Pacific. Despite security needs, this time, the Reagans are telling friends they won't require as large a house.

Whatever the size, the price won't be modest. Abbott said there is a two-bedroom, one-bath home "that needs a little work" selling for $225,000. At the other end of the scale are homes starting around $800,000 and going up into the multimillion-dollar range.

The Reagans will spend three weeks in California, starting Aug. 11. Most of that time they will be at their ranch, but around Aug. 20 they will go to Los Angeles for four days to see their children.