The Maryland special prosecutor's office will investigate a $2,000 loan received in January 1980 by a close aide of Montgomery County Exeutive Charles Gilchrist, State's Attorney Andrew Sonner announced yesterday.

The state probe would mark the first time that law enforcement officials have formally investigated allegations of criminal behavior in the Gilchrist administration, according to Sonner.

Last week former liquor firm exeuctive Charles Buscher testified that in January 1980 he loaned Gilchirst aide Gerard Evans $2,000 to help make a down payment on a house. At the time of the loan, Evans, who has since resigned, and Gilchrist were recommending that the husband of Buscher's niece be hired as deputy head of the county's Department of Liquor Control.

A recently concluded grand jury investigation focused on alleged criminal activity in the liquor department in 1977, before Gilchrist took office, Sonner said. It brought no indictments. Other liquor-related investigations by outside consultants and the county's personnel board have studied allegations of noncriminal misdeeds, such as mismanagement and improper hiring.

Evans resigned his county job in early March, three days after grand jury investigators questioned him about the loan, even though they were not pursuing events after 1977, Sonner said.

Investigators concluded from the interview with Evans that there was no evidence demonstrating the loan constituted a bribe, Sonner said. The loan became public a week ago when personnel board investigators questioned Buscher about it in an open session.

Yesterday Sonner said he had asked state special prosecutor Gerald Glass "to begin an investigation of any possible criminal law violations" involved in the loan. He did not ask Glass to look at other aspects of the liquor controversy, Sonner said.

He sought Glass' assistance after reviewing investigators' notes and press accounts of the loan and deciding his office might not appear sufficiently "objective" to the public. Sonner, a Democrat, ran on Gilchrist's ticket in 1978. The state special prosecutor's office was created in the mid-1970s to investigate allegations of political corruption and multi-jurisdicational crimes.

Glass was not available for comment last night. Gilchrist issued a statement declining comment on a pending investigation but pressing hope that the matter would be "handled expeditiously so as to resolve any questions involving these two individuals."

Buscher testified last week that he loaned Evans $2,000 at 6 percent interest with a check dated Jan. 10, 1980. Evans said later that he put the money down on a house but did not purchase it because of a dispute over terms.

Evans paid the loan back in two cash installments, in October and December 1980, but some interest remained outstanding, Buscher testified.

At the time of the loan, Evans was lobbying a county personnel committee to hire Frank Orifici, then employed by Buscher's firm, Schenley Industries, to be deputy head of the liquor department. Orifici got the job and remains in it today.

In his testimony, Buscher denied he had attempted to influence county officials to hire Orifici. Evans and Gilchrist meanwhile have said that they felt Orifici was the best man for the job and made their views known to officials making the selection.

Buscher's disclosure gave new life to the liquor controversy, which had dropped to a low key in recent months after the grandy jury and an independent auditing firm gave generally good marks to the Gilchrist administration concerning the liquor department.

Local Republicans had been discussing making formal requests for new investigatiions by state and federal authorities.