The federal government says it is ready to sell two parcels of unneeded property at the Beltsville Agricultural Research Center to a state agency, but Sen. Charles McC. Mathias (R-Md.) has thrown a monkey wrench into the plan.

Mathias Feb. 3 introduced a one-paragraph bill into the Senate that would bar the sale, conveyance or lease of the two properties. He said he opposes the sale because an eighth of the federal reserve already has been sold. The properties include a 247-acre parcel on Odell Road that has been used for insect studies and a 13-acre parcel on Rte. 1 that has been used for turf experiments.

General Services Administration officials in charge of the sale say that out of courtesy to Mathias the deal with the Maryland-National Capital Park and Planning Commission may have to be put on hold if the senator proceeds with hearings that he is considering and notifies GSA of his intentions.

"The two . . . parcels will be developed and utilized primarily for public administrative, educational, institutional, economic development and recreational purposes," said Charles A. Dukes, the commission's chairman, assuring the GSA that "funding sources are currently available" for the purchase.

Under law, public bodies, such as the commission--a bi-county agency formed by the state of Maryland--may ask for negotiating rights to unneeded federal lands before they are offered for sale.

The commission was the only agency to submit an offer before the deadline, but GSA said the city of Greenbelt has also indicated an interest in buying the land. The city's letter of interest arrived after the Feb. 3 cutoff, however.

"This land and the research center . . . have been an important part of the nation's effort to make agriculture more productive, both in the United States and around the world," Mathias said of the 73-year-old facility. "To our shame, the federal government is selling our national patrimony."

The sale of the two tracts is part of the Reagan administration's stated intention to manage the nation's property assets in a more businesslike fashion. To further that goal, GSA plans a one-month survey of the rest of the 8,000-acre facility beginning April 19 to determine whether all of it should be sold.

Earl E. Jones, the GSA's assistant commissioner of real property, said he was "not surprised" Mathias moved to block the sale, although GSA congressional affairs officials had not informed him the bill had been introduced.

"Normally, if there is a request from a committee chairman, we'll put a hold on the sale," Jones said. "But we haven't got one yet."

Jones said negotiations with the park and planning commission will begin after an appraisal of the two properties is completed in March, unless "higher-ups" decide to put a hold on the deal.

John W. Eddinger, Mathias' press secretary, said the senator plans to hold hearings soon on the disposal plans for the research center.

Eddinger said he hoped the GSA would voluntarily hold off on the commission sale until those hearings are complete, although there has not been a formal request to do so. "If they go ahead, they're doing something risky," he said.

Adding to the confusion is a pending request from Maryland state archaeologist Tyler Bastian, who has asked the GSA to postpone the sale until a federally required archaeological survey is completed.

Carroll Jones, the GSA's commissioner of federal property resources, said the Agriculture Department has been notified that the archaeological survey is required.

In addition, Jones said, the "GSA is preparing an environmental assessment of the property so that all archaeological and historical factors will be fully considered before final disposition."

The Capitol Institute of Technology, a school that is opening a new campus on land near the 247-acre tract, has written GSA property-disposal officials in Atlanta that it is interested in obtaining the land free to use in ecological studies.

"The college's use of the land would maintain an important natural asset of the region and allow it to enhance its academic program," said G. William Troxler, the institute's president, noting that for the past six years the land has been used to support field research on rare and endangered species.

Jones said last week the agency had not received the letter.