Next time the conversation turns to Washington's favorite topic, the price of houses, think big. Think of the District government's list of the 10 most valuable residential properties in the city, and you'll get a new perspective on your own cozy brick rambler 3 br mod kit.

The list, compiled by the Department of Finance and Revenue, begins with the least of the most, the estate of Gwendolyn Cafritz at 2209 Foxhall Rd. NW, valued at $1.4 million -- and goes up. At current rates, Cafritz heiress to a real estate empire and long one of the city's most prominent hostesses, is paying more than $17,000 a year in property taxes.

Hers is the lowest valued at the top 10, but it is also one of the few still intact and still lived in by the family whose name is associated with it. Other properties on the list are already being subdivided or removed from residential use. The Washington estate is going the way of the ocean liner and the grand tour.

Under the District's tax system, assessed valuations are supposed to equal real market value. Since valuations on the top 10 list were for the year 1979-80, the assessments shown have been raised since the list was compiled.

At the top of the list is Hillwood, the lavish 25-acre estate of the late cereal heiress Marjorie Merriweather Post. Located at 4155 Linnean Ave. NW, overlooking Rock Creek Park, it was converted to a museum in 1977 but is still zoned for residential use and carried on the tax rolls. City assessors calulated its value at $4.85 million.

Hillwood has moved into first place ahead of the long time titleholder, Hillandale, the 42-acre Archbold estate adjacent to Georgetown University Hospital at 3901 Reservoir Rd. NW. That property is assessed at $4.83 million, but it is being cup up into town house lots. When the town houses are complete, the tax revenue for the city will increase because the cumulative value of the new houses will exceed that of the estate with its single mansion.

The other properties on the city's list are:

Tregaron, the estate of the late ambassador to Moscow Joseph P. Davies (who was once married to Marjorie Merriweather Post) at 3100 Macomb St. NW. in Cleveland Park. That property assessed at $3.1 million, was sold last fall for $4.6 million to developers, who plan to leave the main house intact for use by a private school and build 200 town houses on the rest of the site.

The house and grounds formerly owned by late Vice President Nelson A. Rockefeller at 2500 Foxhall Rd. NW., assessed at $2.9 million. The house is now owned by R. Sargent and Eunice Kennedy Shriver. The rest of the 27-acre tract is being sub-divided into 26 lots for luxury houses in a development called Foxhill Crecents, but is still taxed as a single property.

A vacant lot at 50th Street and Massachusetts Avenue NW, in Spring Valley, owned by the W.C. and A.N. Miller Development Co., valued at $2.7 million.

A group of houses on secluded Battery Place NW, the quiet Potomac Palisades enclave where Washington cardiologist Michael Halberstam was recently shot to death by a burglar. Though they look like other single-family homes, they are legally a single cooperative and taxed as one property, valued at $2.6 million.

The estate of Geico insurance tycoon and art collector David Lloyd Kreeger at 2401 Foxhall Rd. NW. That house, an architectural landmark whose gently curved domes catch the eye of every Foxhall Road motorist, is valued at $2.3 million.

The spectacular European style manor house and extensive grounds of an estate at 1801 Foxhall Road NW. owned by Elinor Brady, widow of Rear Adm. Parke H. Brady, former headmaster of the Sheridan School. It is assessed at $2.2 million.

A vacant eight-acre tract on Reservoir Road NW owned by the government of France, valued at $1.7 million.

For overall value, none of the residential properties is in the same league with the major commericial and development properties in the city. The leader is L'Enfant Plaza, assessed at $78 million, which has overtaken the Watergate complex at $74.8 million. CAPTION: Picture 1, Hillwood, the lavish estate of the late Marjorie Merriweather Post, at 4155 Linnean Ave. NW is valued at $4.85 million. By Richard Darcey -- The Washington Post;ntemporary home, an Picture 2, Tycoon David Lloyd Kreeger's contemporary home, an By architectural landmark with curved domes, is valued at $2.3 million. By Harry Naltchayan -- The Washington Post Picture 3, The Tregaron mansion will become a private school, surrounded by 200 town houses. By James McNamara -- The Washington Post; Picture 4, The home of Gwen Cafritz,located at 2209 Foxhall Rd. NW, is valued at $1.4 million. By Vic Casamento -- The Washington Post Picture 5, Hillandale, 3901 Reservoir Rd. NW, assessed at $4.83 million, is being cut up into lots. By Larry Morris -- The Washington Post