Officials of the Merchandise Mart of Chicago have signed a preliminary agreement with the District of Columbia for exclusive negotiation rights on a 240,000-square-foot site at Fourth and D streets SW.

To secure the option, which expires May 1, Mart negotiators paid a $100,000 deposit toward the $3 million property, a seven-story facility built in 1920. The building would be used to house 200 to 250 furniture display showrooms.

"We are very excited at the prospect," said Ann Kinney of the District's office of Business and Economic Development. "We have every expectation that they [the Merchandise Mart] will come, but the deal has not been concluded and is ongoing. They are about halfway through the negotiations."

Among the major enticements are the availability of public transportation and hotel facilities, she said. The Metro has a Blue Line Stop at Seventh and D streets SW, and the Orange Line has a stop at the Federal Center, Third and D streets SW. To accommodate furniture buyers, the proposed Mart site is near the $100 million Holiday Inn Capitol, which opened last December with 529 rooms and parking for guests at 550 C St. NW.

According to Larry Schumake, executive director of the Office of Business and Economic Development, the Mart project would total $20 million, including construction of an additional 190,000 square feet of space. During the construction phase, an additional 180 jobs would be created with 515 permanent jobs envisioned eventually to staff the showrooms. Annual revenue to the city is projected at $3.3 million, Schumake said.

Mayor Marion Barry has been actively involved in courting Mart management since it first indicated its interest in a Washington-area site. After the Mart set a ceiling on the amount of money prospective tenants would be willing to pay in rents, the city took the initiative in scouting available properties, Schumake said.

The world's second-largest wholesale buying center, the Merchandise Mart complex houses 6.5 million square feet of space. The Mart itself encompasses 4.2 million square feet, or the equivalent of 97 acres. (The Dallas Market Center with 7 million square feet became the largest in 1979.)

Originally built by Marshall Field & Co. in 1930 at a cost of $32 million, the building was purchased in 1945 by the late Joseph P. Kennedy and currently is owned by the Kennedy family. The District project is the Mart's first official foray beyond its Chicago headquarters.

Larger than some towns, the Mart is staffed by 28,000 people for its daily operations, with that number swelling to 60,000 during major market shows. Annual sales by Mart merchants are estimated at $5 billion.

Jackie Moore, a spokeswoman for the Redevelopment Land Agency, said the original public hearings on the site had been shifted from March to an unspecified date in July. The purpose of the meeting is to tell neighbors and the public what the Mart would do to renovate the site, she said.

Should the project win approval, construction could begin later in the summer. Schumake said, with occupancy slated for some time in 1982.

The Chicago move is one of several Schumake has been encouraging since he joined the District's development office last May. Formerly a developer with a Los Angeles firm that specialized in industrial and shopping center complexes, he also was involved actively with Rouse Co. of Columbia.

During 1980, his office averaged 50 new contacts a month with prospective businesses, and some particularly good months brought the annual total to 900.

His office operates a staff of nine and a budget of $711,000 in its search for District tenants. Some congressional funding also is provided, Schumake said.

During the five-year period from 1965 to 1970, one out of every three Washington-area residents moved into or out of the region. Thus the Washington metropolitan area had the highest rate of population turnover among the nation's 10 most populated areas.

In fact, Washington's proportion of migrants was 75 percent about the national average of the nine other top markets. In addition to cross-country moves, there is a fairly frequent current of relocation within the District, Virginia and Maryland.

A major impetus for buying new furnishings is moving. Often it is easier to pitch out an old sofa, the slightly frayed kitchen curtains and that old hunk of bedroom carpeting rather than lug them to a new location.

Likewise, mobility can denote a change in status with the accompanying need for new furniture. If one goes from being single to married or vice versa, for example, there may be a need for a new bedroom set and kitchen things. If you go from nonparent to parent, you'll need cribs, cradles, dressers, changing tables, car seats, play tables, toy boxes and storage units.

If you become an empty nester, you need furniture of a different scale since the sprawling family home may have been filled with huge Mediterranean pieces that won't get through the door of your compact new high-rise condominium.

Washington is a mobility mecca, hosting military, foreign, political and business people who move often because of jobs. People may rent or buy furniture here and keep other possessions in storage in faraway cities.

Nearly half of all the Washington-area households enjoyed incomes of at least $20,000 in 1977, with more than a quarter having incomes of $30,000 or more. "Washington's household income distribution demonstrated a broad-based affluence which continues to be unmatched by any other market," according to Post researchers.

For retail sales, Washingtonians spent $12.5 billion in 1978, a 13 percent increase over the previous year. This averaged $11,624 per household, an increase of 9.4 percent from the previous year.

In the area of furniture, home furnishings and appliances, Washington ranked fourth nationally among all major markets for household spending, with an estimated $642.5 million -- a quantum leap of 158.3 percent over the 10-year period from 1968 to 1978.