Bethesda-based Marriott Corp. and Chicago's Pritzker family have been pursuing a joint buyout of Allegis Corp., the parent company of United Airlines, Hertz Corp. and the Westin and Hilton International hotel chains, sources close to the negotiations said yesterday.

If Marriott and the Pritzkers, who own Hyatt Hotels Corp., succeed in buying Allegis, the two interests would be likely to divide the Westin and Hilton International properties between them and sell off the airline and the car rental company, according to financial sources.

The cost of such a takeover has been estimated by analysts at about $7 billion. By buying all of Allegis and selling off the nonhotel properties, Marriott and the Pritzkers would probably get the hotels for a better price than by bidding for them separately, sources said.

A Marriott Corp. spokesman said yesterday that Marriott "is not currently involved in any negotiations regarding Allegis." However, industry sources confirmed that Marriott and the Pritzkers have been involved in discussions for Allegis as recently as last week.

Marriott -- the Washington area's largest corporation, with $5.2 billion in sales in 1986 from its hotels and food services -- last year bought Saga Corp. for about $700 million and recently has been negotiating to buy Residence Inns.

Asked whether the Pritzkers are discussing a joint bid with Marriott, Darryl Hartley-Leonard, president of Hyatt Hotels Corp., said: "If that's true, I don't know it." Representatives of Allegis could not be reached for comment.

The Pritzker family, which also owns Braniff Airlines, began to buy a stake in Allegis several months ago, at about the time the United pilots union put the company into play by proposing to buy United for $4.5 billion. Representatives of the union have said they will continue to pursue employe ownership of the airline, and sources said yesterday that both Marriott and the Pritzkers would want to sell the airline.

"Everything in this area is premature because the airline pilots haven't been able to get financing," said John Peterpaul, vice president of transportation for the International Association of Machinists, which opposes employe ownership of the airline.

Representatives of the pilots union could not be reached for comment yesterday.

A large number of buyers are said to be interested in the two hotel chains Allegis owns, including Hilton Hotels Corp., which is unrelated to Hilton International, and Japanese and British groups. Analysts have estimated that the two chains, which have been consistently profitable, are currently worth about $2 billion.

Both Hilton International and Westin are valuable for their real estate as well as for their hotels. New York real estate developer Donald Trump has reportedly said that New York's Westin Plaza alone would be worth $750 million if it were turned into condominiums.

One drawback to an existing hotel chain buying either Hilton International or Westin is that it might result in duplication in cities where a chain has a competing hotel, according to analysts. However, if Marriott and the Pritzkers divided up the hotel properties, each could get hotels in cities where they don't currently have them.

Marriott, which has 13 hotels outside the United States, has long been interested in expanding its international presence -- a difficult task in many European and Asian cities where there is little land for new construction. Industry sources have said that the Westin hotels in Japan, Canada and Hawaii are of particular interest to Marriott.

Marriott currently owns more than 200 hotels and resorts, while Hyatt Hotels Corp. operates 80 hotels in the United States, Canada and the Caribbean. Hyatt International, a separate company, and its subsidiaries operate 41 hotels in 25 other countries.

Marriott has 14 hotels in the Washington area. Hyatt currently has six, with two under development here.

The Vista International, operated by Hilton International, and Westin hotels in downtown Washington are among the area properties owned by Allegis.

Allegis Corp. became a diversified travel services company under Richard J. Ferris, who was forced to resign as chairman June 9. The company's new chairman is former Hertz Corp. chairman Frank A. Olson.

The Allegis board has said it hopes to devise a plan to sell off the various parts of the company in a way that will maximize the company's value to shareholders. Ferris had opposed efforts to split up the conglomerate. Staff writers Martha M. Hamilton and James L. Rowe also contributed to this report.