The owner of a private security agency, based in Springfield, was found guilty by a federal jury yesterday of hiring a man previously convicted of armed rape and allowing him to carry a pistol while working as one of the firm's security guards.

Charles R. Quillin, a former District of Columbia policeman who now owns Metropolitan Protective Services Inc., the Springfield-based firm, was convicted of all nine counts of an indictment that also accused him of lying to a grand jury about the incident. Other counts in the indictment charged Quillin with carrying a pistol without a license.

Quillin, who was a D.C. policeman from 1969 to 1974, later set up the security firm, which eventually included 60 employes. Among the businesses for which Quillin's firm had provided security guards was American Security Bank.

As a result of his conviction in U.S. District Court here, Quillin faces a maximum sentence of 31 years in prison, $42,000 in fines, or both.

Quillin's conviction followed guilty pleas by two other men who had been indicted in connection with the incidents.

Quillin's brother, Robert, who had worked for Quillin's security agency, pleaded guilty at the start of the trial Wednesday to two counts of carrying a pistol without a license. He faces possible penalties of up to two years' imprisonment, $2,000 fines, or both.

Michael W. Carey, the security guard who had previously been convicted of armed rape, pleaded guilty March 31 in D.C. Superior Court to a single misdemeanor count of carrying a pistol without a license.

Federal prosecutors agreed to drop felony charges against Carey in exchange for his testimony against Quillin. Carey could be sentenced to up to a year's imprisonment, a $1,000 fine, or both on the misdemeanor court.

William J. Hardy, the assistant U.S. attorney who prosecuted Quillin, produced evidence to show that Quillin knew Carey was a convicted rapist and that Quillin, nevertheless, told Carey to carry a pistol while working as one of the firm's guards. It is illegal for a convicted felon to carry a gun.

Quillin, who testified in his own defense, denied all the prosecutor's charges, contending that he did not know Carey was a convicted rapist and did not tell Carey to carry a gun while working in the District of Columbia. Quillin also testified that he himself had not carried a pistol in the District, where he could not legally do so except in a security officer's uniform.

The federal investigation of Quillin and his firm began last fall when Carey was stopped by police on a routine traffic charge.