Dulles International Airport trails in the fierce nationwide competition to land a $500 million United Airlines maintenance facility, but area officials say they are scrambling to put two eleventh-hour proposals on the table in an effort to close the gap.

Legislation permitting Virginia to subsidize the airline's construction financing costs at Dulles will be introduced in the Virginia General Assembly in January, and private landowners may donate 300 acres for the plant just west of the airport in Loudoun County, Virginia officials told the airline this week.

Considered one of the largest economic development projects planned in the United States, the plant will supplement United's West Coast maintenance facilities. Opening in phases beginning in 1993, the new plant will employ up to 7,000 people.

The facility will provide a major economic stimulus to the winning locality at a time of stagnation and cutbacks. Officials in Virginia say they believe that Dulles is about fourth on United's list of locations under consideration, and the airline expects to announce a decision soon.

"It appears that Virginia may not have on the table a proposal as strong as do some of the sites United is considering," said state Sen. Charles L. Waddell (D-Fairfax/Loudoun) this week.

Aggressive financing subsidies reportedly offered by other cities could be worth as much as $50 million, some officials said. State law bars such assistance from Virginia. Two Kentucky sites -- greater Cincinnati and Louisville -- are generally believed to be near the top of United's list. Other cities mentioned as contenders include Tulsa, Oklahoma City and Denver.

United is known to be concerned about timely and convenient access to Dulles and the shortage of low-cost housing in Loudoun. However, United's choice of Dulles as an East Coast hub, its construction of a reservations center in Loudoun and its plans to increase international flights from Dulles have been cited as pluses for the airport's bid.

The late scrambling by Dulles backers occurs about six weeks after the Loudoun County Board of Supervisors split publicly over the value of roads and water and sewer lines that the county should pledge for the maintenance project. Since then, the Loudoun board has sought General Assembly approval to establish a new local tax category for the plant that would be more favorable to United.

Some area officials have questioned whether too much is being offered to United, saying the deal might not be lucrative to the Dulles area in the short term. Loudoun County has pledged millions of dollars for roads and utilities to the plant, prompting county Supervisor Betsey Brown (D-Catoctin District) to ask, "Where is it going to come from?"

An attorney for Emmanuel Holdings and Eugenia Investments confirmed that the two investment firms are considering donating 300 acres of a 1,200-acre parcel west of the main Dulles terminal and cargo area. County officials said the United plant would boost the value of nearby private land.

In a recent letter to state legislators, Gov. L. Douglas Wilder said Dulles would have a better chance if the state government "could provide funds to improve the credit rating or reduce the interest rate" on construction bonds.

"If purchased through a financial institution, such a credit enhancement could cost as much as $25 million in state funds," Wilder wrote in asking that House and Senate money committees hold hearings on such a precedent-setting program for Virginia.

This week, state senator Waddell said he will sponsor emergency legislation permitting such a subsidy and will ask United to hold off on a site selection until the legislature acts.

Negotiators for United had indicated that Loudoun, Virginia and the Metropolitan Washington Airports Authority "had put nothing tangible on the table recently," said Waddell, adding, "Obviously, you can't give away the store."

Choosing Dulles for the maintenance plant "would help to ensure that Dulles would become the premier international gateway on the East Coast," Wilder told legislators recently.