A Montgomery County Mercury dealer has signed an agreement not to pocket customer rebates and will pay $5,000 in civil penalties, consumer investigators said yesterday.

B.M. Woodfield Mercury of Damascus and Michael Woodfield, the firm's manager, allegedly failed to turn over rebate checks to a least seven car buyers, according to the Montgomery County Office of Consumer Affairs. The rebates, totaling $2,500, have now been received by the buyers, officials said.

Manager Woodfield, who signed the cease-and-desist agreement without admitting any violation of county consumer protection laws, blamed the aebate complaints on "poor communication between salesman and customer." He said his dealership shut down in October 1980.

Marjorie Wax, the investigator who handled the case, said seven Woodfield customers has waited nearly a year from their rebates, ranging from $200 to $1,000. Among them was Willard Groomes, a Frederick County man who brought a 1980 Zephyr from Woodfield Mercury in March 1980.

"I waited a month and when it didn't come, I went and talked to the salesman," Groomes said. "The salesman said the check was coming, but it never did, so I went to the consumer affairs office and complained."

Groomes received his $300 rebate last week.

In releasing the agreement, the consumer affairs office alleged that Woodfield Mercury also had:

Issued false lien releases indicating that there were no unpaid liens on used cars being sold when in fact money was owed and the titles were not free and clear.

Issued a false Maryland state safety inspection certificate for a used car.

Misrepresented the actual mileage on a used vehicle.

Investigator Wax said that the dealer had agreed to cease and desist from engaging in those or any other deceptive practices as defined in a consumer protection law and to submit to binding arbitration any complaints against the firm that the consumer affairs office cannot conciliate.

Woodfield denied those allegations yesterday. He said he had signed the agreement because the consumer investigators, Wax and George Rose, "were very, very nice and the consumer affairs office was very fair, so we decided to work with them."

Barbara B. Gregg, director of the consumer office, said that it is important for consumers to know and understand all the terms involved in rebate programs. She said anyone having a problem obtaining a rebate from a Montgomery County dealer should contact her office at 279-1776.