The Fairfax County Board of Supervisors ordered the county staff yesterday to review a proposal under which a private developer would be given land in exchange for building a new government center, and to compare the cost with other financing options, such as bonds.

The board also voted to allow a private firm to build and operate a $250 million trash incinerator at the Lorton landfill.

Critics of the proposed government center land swap have complained that the county would not get its money's worth. Under the proposal, the Charles E. Smith Cos.-the Artery Organization Partnership would build an $83.4 million government center on 100 acres near I-66 and Rte. 50 in exchange for 116 acres of adjoining land, $24.6 million in cash and $16.6 million in other forms of compensation. The entire government center complex is 216 acres, 183 acres of which the county bought for $4.1 million in 1979. The 116 acres involved in the land swap has been valued at $42 million.

Critics say the county should finance the project with bonds and keep the land, which they believe will be worth substantially more once the government center is built.

"I think it's real important that we get on the table for the world to see what the options are," said Supervisor Thomas M. Davis III (R-Mason). "If one way is much cheaper than the other, I think we've got to go with it. But we need to say from looking at the alternatives that this is in the county's best interests for such-and-such reasons."

The staff was asked to compare the cost of the land-swap proposal with the cost of three alternatives: financing all of the project with bonds, financing $58.6 million of it that way and auctioning off 66 adjacent acres. The staff also was asked to gauge the impact of each option on the county's general fund and to estimate the value of the adjoining land once the government center is completed.

The Fairfax County Federation of Citizens Associations maintains that the county could save as much as $135.8 million by financing the project with bonds. However, many supporters of the partnership with Smith/Artery argue that the county should reserve its bonding authority for roads and schools.

On the incinerator issue, construction of a trash incinerator at the landfill was approved a year ago despite the objections of area residents.

Yesterday, the board voted 7 to 1 to authorize County Executive J. Hamilton Lambert to sign an agreement with Ogden Martin Systems to build, operate and maintain the facility. Construction is scheduled to begin this winter.

Officials said the facility, which will be one of the largest in the country and able to handle 3,000 tons of trash daily, will be safe.

Supervisor Nancy K. Falck (R-Dranesville) called it "environmentally sound," while Supervisor Audrey Moore (D-Annandale) said it would be equipped with special filters and "scrubbers" to remove acid gases.

Supervisor T. Farrell Egge (R-Mount Vernon), who represents Lorton on the Board of Supervisors, voted against the motion. He said later that the area "has been traditionally the place to dump stuff" in the county and that he favored building three smaller facilities in separate locations.

In working out the agreement with Ogden Martin, the board created a county Solid Waste Authority, with the supervisors as its officers, Lambert said. The authority can issue low-interest, federally tax-exempt industrial development bonds.

The incinerator will reduce the amount of trash dumped at the landfill by about 80 percent, according to public works director John W. diZerga, and will be able to produce electricity from the burning of garbage. Virginia Power has agreed to buy the electricity, with Ogden Martin and the county sharing the proceeds, according to a staff report. The county expects to receive about $20 million annually under the agreement.

Also yesterday, the board voted 9 to 0 to modify the charter of the Southeast Fairfax Development Corp. in response to complaints that the publicly funded group has barred people from its meetings, refused information to the public and sided with developers on contested projects.

Under the changes, two citizens groups on the corporation's board will each get an additional seat, board members will have to file financial disclosure forms and the organization must amend its procedures for notifying citizens about meetings. But the corporation will not have to identify the source of its private donations, as some critics had proposed.

The corporation was formed as a public-private partnership in 1982 to support economic development in the Rte. 1 corridor between the Capital Beltway and Fort Belvoir. It has received about $800,000 in county funds.

Also yesterday, the board ordered the staff to review procedures that allow new developments costing more than $25 million to be "fast-tracked" through the site-review system. The action was taken after supervisors questioned the fairness of the policy and said it could be dangerous because allows construction to proceed before inspectors have copies of the final site plans.