Montgomery Country police are investigating a motorcycle patrolman who was in charge of tow-away operations in Silver Spring who testified in court last month he had been loaned $1,000 from a Silver Spring tow truck operator.

The testimony of Officer John A. Porter, a 12-year veteran on the county force, came at the trial of Douglas L. Sanders, who was subsequently convicted of attempted murder and solicitation to murder an Internal Revenue Service tax investigator in a murder-for-hire plot.

Porter, called as a defense witness, first testified that he was present during a meeting between Sanders and a man whom Sanders allegedly hired to kill the IRS man. He said he heard no discussion of a murder plot.

Under cross-examination, Porter was asked if he had ever received money from Sanders, proprietor of Dial-Tow, one of about 20 concerns used by police in Silver Spring to haul disabled and illegally parked vehicles.

He testified he received loans totaling $1,000. "At the time of the loans I was on disability leave from being injured on the job," he testified. "I was in strait financial conditions and had not been able to work my normal part-time job, which is a necessity . . . I needed the money." He said he had paid back part of the money and intended to pay back the rest.

Francis L. Coffren, an internal affairs investigator for the county police department, testified the next day that Porter was already under investigation for matters other than the loans from Sanders and said it would be a violation of the county code for someone in Sanders' position to accept loans from the owner of a towing firm. Porter is no longer in charge of towing operations.

Capt. Owen Bromley, commander of the Silver Spring station, said he requested an internal investigation of Porter "about a year ago" but declined to comment further.

Neither Porter, who continues on active duty at the Silver Spring station, nor his attorney, Paul Stein, would comment yesterday.