That the Spanish Embassy is interested in buying the Codman House (2145 Decatur Place NW) for the ambassador's residence surprises no one. Few houses of its dimensions and desirability in the District have escaped occupation by foreign powers, becoming tax-free, extraterritorial mini-states.

The 1906 four-story red brick-and-stone mansion earned its line in the National Register of Historic Places, with distinguished architecture by Ogden Codman Jr.

The Codman House stands just to the east of the Spanish Steps, which run between Decatur Place and S Street, in a manner reminiscent of the Piazza di Spagna in Rome.

If the romantic Spanish need one more reason to buy, the chandelier-lit salons of the Codman House echo with the notes of a love song of the late 1920s, the autumn/spring romance of Martha Codman, a cousin of the architect who commissioned the house and lived in it in the early years of the century.

So far, the Spanish Embassy has yet to emboss its royal seal on a sales contract, but administrative attache' Juan Murrieta admits his government is "interested" in buying the house for the ambassador's residence. "We haven't made an offer -- yet," he said. "But we are thinking of moving." Since 1926, the Spanish chancery and residence have been at 2801 16th St.

The Spanish have flown over experts to assess the house, measure and poke and smile a lot. One hurdle has been jumped. Calvert Bowie (Bowie Gridley Architects) designed a garage addition that wouldn't violate the National Trust for Historic Preservation easement placed on the house by previous owner Stellita Renchard. In the '70s, she bought it to save it from becoming a 30-unit condominium.

Standing first on one foot and then another, waiting for the peseta to drop, are Martha Fleming, (Randall H. Hagner and Co. real estate brokers) listing agent; Carole Hersman, of MGMB Inc., hopeful selling agent; and Tom Torr, the house sitter.

Even the neighbors, asserts Hersman, are hoping the Spanish will buy the house. Kalorama is already a refuge for well-provided Americans, including Polly Logan. (Her former Forest Hills estate, Firenze, is now the Italian ambassador's residence.) Kalorama is also an international enclave of ambassadorial residences: The Chinese, French and Irish are just up the Spanish Steps, near the Textile Museum and the Woodrow Wilson House Museum.

Even with its $3.5 million price tag, it's surprising that the Codman House has stood empty since 1976.

Imposing proportions and spacious terraces define this as a true town residence of the old school. It withdraws behind its ornate gates into an arrival court of French yellow brick in a herringbone pattern. The tall, shuttered windows on the second floor are arched at the top, designating it from the outside as the piano nobile, or principal floor.

Up the oculus-lit staircase are a paneled library, music room, drawing room and dining room, all with original chandeliers, sconces, marble mantels ...

Its current owner, a mysterious Italian on record only as Decatur Place Enterprises, added a swimming pool where the conservatory once bloomed.

The name of Codman House derives from both its architect, coauthor with novelist Edith Wharton of "The Decoration of Houses," and its builder, his cousin.

Martha Codman, heiress to a Boston family whose clipper ships came in bearing the wealth of the world, came to Washington, as National Trust historian Suzanne Ganschinietz said, "during the spectacular age of elegance in Washington, 1870 to 1930, when the nation's capital became the winter Newport of America." She was heiress to a Boston family whose clipper ships came in bearing the wealth of the world.

Her Washington mansion was built for entertaining -- dinners, balls, teas, musicales. After 70 independent years, Miss Codman met, perhaps in her music room on Decatur Place, the 30-year-old singer Maxim Karolik, a Russian who narrowly escaped the Russian Revolution. In 1928, they married and lived happily ever after.

In 1938, former Philippines governor general Dwight Filley Davis (of the tennis cup) bought the house. In 1947, it became the Louise Home, founded by W.W. Corcoran (of the gallery) for ladies "who had known brighter days and fairer prospects ... compelled to contend with adverse circumstances." After the Louise Home's organizational merger with the Lisner Home, the Codman House went on sale once again.

Stellita Renchard, whose house at the top of the Spanish Steps overlooked the Codman terraces and house, bought it (for $500,000). Renchard worried about ownerless houses the way some worry about homeless cats. She had hoped to preserve the house by making it into a museum for her Spanish American art collection. Tragically, she and her husband, former ambassador George Renchard, were killed in an automobile accident in 1982. The Columbia Historical Society remembers them with the annual Renchard award for preservationists.

Perhaps the Spanish will earn the award next year.