The Alexandria housing authority is asking for bids on the last chunk of land in the urban renewal project named the Dip, which covers about 12 blocks in the city's historic Old Town.

The triangular-shaped piece of land is the 1000 block of Duke Street on the south side, between Patrick and Henry streets.

The property is divided into 12 lots, with 11 of them fronting on Duke Street. These are zoned for commercial business use and must be developed in Old Town townhouse style, regardless of interior use, said Tom David, chief of the rehabilitation division in the Office of Housing.

Two of the smallest lots, at 1018 and 1020 Duke Street contain two houses that are on the city's list of 100-year-old properties. These buildings must be rehabilited and preserved, he said.

The remaining plot contains 50,791 square feet of land on which an office building or hotel could be built, he said.

The city hopes to see the property developed into "an attractive gateway to Old Town," added David.

Although the property belongs to the Redevelopment and Housing Authority, proceeds of the sale by law must go to the Dip project. Any money left over would go to the city's Community Development Block Grant, said David.

Work in the Dip project started in mid-1971, and is either completed or under contract except for the block now for sale, he said. Residences cover nearly all of the Dip area; some are subsidized dwellings while others sell for prices ranging over $100,000.

Appraised value of the land is $15.57 per square foot. The lots can be sold singly or as a package, said David. Developers will be required to hire an architect who is experienced in Old Town construction. If purchasers go to settlement before Nov. 12, 1984, they can get the property with a 25 percent down payment, and the city will carry the remaining 75 percent until that time. Then, the buyer can pay the balance of the payment for the property, plus interest, at 10 percent a year or 50 percent of the prime rate at a bank agreed to by both parties, whichever is higher.

Deadline for bids is March 10. The city expects to award contracts by April 15.