The D.C. Office of Campaign Finance has begun an investigation to determine whether city Rent Administrator John Hampton violated any D.C. ethics law by accepting a home purchase loan from a former Washington Board of Realtors official.

Keith Vance, director of the campaign finance office, began investigating Hampton's loan last week after learning about it from a reporter, according to a source. Vance declined to comment yesterday.

Hampton received the loan in 1981 in the form of a deed of trust for $9,600 on a house that James G. Banks, a lobbyist and then-executive vice president for the Washington Board of Realtors, sold to Hampton for $25,000. Hampton, who was then the special assistant to the rent administrator, and Banks said they had been friends for years and saw no conflict in the transaction.

On Tuesday, a lawyer representing one of Hampton's employes who was fired for an alleged conflict-of-interest violation, filed a formal complaint with the city requesting that the D.C. Department of Consumer and Regulatory Affairs, the D.C. corporation counsel and Vance investigate Hampton's loan.

Norman Smith, the employe, was fired for requesting and receiving a $3,000 loan from a landlord whose property fell under the jurisdiction of the Rental Accommodations Office. The office administers the city's rent control law.