A group of Washingtonians has filed a class action against two District financial institutions, charging that they held up settlement payments to home sellers and thereby unduly benefitted themselves.

On behalf of sellers Adam Yarmolinsky, Jonathan and Eleanor Lash, and all District homeowners who have sold houses within the past three years, the Public Citizen Litigation Group filed suit Thursday in D.C. Superior Court against Perpetual American Savings and Loan Association and American Security Bank. According to the brief, Yarmolinsky received his payment from Perpetual 17 days after the settlement date. He estimates an interest loss of about $400 on the $119,000 mortgage that was financed through Perpetual.

Jonathan and Eleanor Lash, who sold their Washington home in June 1978, received a check for $96,000 from American Security Bank 10 days after settlement. They estimate their interest loss at something under $200. The lenders were, of course, receiving interest from the buyers on the loan during that same period.

Fred Townsend, the plaintiffs' attorney, noted that Maryland and Virginia both have so-called "wet" settlement laws, meaning that the seller's check has to be presented at settlement. The District does not.Moreover, he added, Maryland law prohibits a lender from charging a buyer interest if the lender has not paid the seller.

Since such dilatory payments are not against District law, Townsend decided the legal basis for the suit would be the validity of the contracts. In addition to the contract between buyer and seller, there is also the mortgage agreement between the buyer and the lender. His reasoning is as follows: one of the purpose of the contract between buyer and lender is to benefit the seller. Therefore if a lender breaches this contract (by sending the settlement check late), then the seller has the right to take action against the lender.

Thomas J. Owen, chairman of Perpetual, said that in many cases title attorneys do not provide the exact amount of the payment until after the settlement because it takes them some time to get information such as water meter readings and tax liens. Owen added that after the information has been received, it takes about 24 hours to process the check. If it is mailed to the seller, the elapsed time could be another three or four days. American Security Bank had no comment.