The General Services Administration last week rejected a $417,500 offer for Ashford Farm, a former CIA safehouse on Maryland's Eastern Shore. The 25-room brick mansion near Easton-where U-2 pilot Francis Gary Powers stayed in 1962 after his release from the Soviet Union-will be put up for bids.

Bayview Associates, a group of five Washington-based investors, originally submitted the top offer of 37 bids received last month. Robert Irwin, a GSA real estate specialist, thought the propoerty, which has 2,000 feet of shoreline on the Choptank River in Talbot County, was worth more. He asked the group, which had bid $407,900, to improve its offer, but the resulting bid was not to GSA's liking.

Irwin declined to say what the agency would consider acceptable or what the property is worth. The CIA bought the estate in 1951 for $68,000. The property is said by local real estate agents to be in need of extensive repairs.

In Somerset County, also on the Eastern Shore, another important brick mansion is up for bids. Almodington, which dates from 1662, will be auctioned April 10 at 2 p.m. at the Princess Anne Courthouse. The 15-room manor house (1670) lies on Manokin River, near Tangier Sound, about three hours drive from Washington and Baltimore.

The 203-acre property was part of 1,000 acres originally deeded to John Elzey by Lord Baltimore in 1662. The early Georgian style house has nine fireplaces and a three-car garage and the property includes a nine-room caretaker's house. The land is zoned for agricultural use.

The present owner, George Ritter, who has defaulted on the mortgage, paid $500,000 for the property three or four years ago, according to attorney Thomas S. Simpkins, who is handling the sale.