Riggs National Bank has sued financially troubled parking garage and real estate magnate Dominic F. Antonelli Jr. for repayment of a $3.7 million debt, further complicating Antonelli's efforts to restructure hundreds of millions of dollars of loans.

The lawsuit filed last month in U.S. District Court said that Antonelli and his wife Judith D. Antonelli failed to repay the $3.7 million after Riggs demanded payment on July 16.

In documents filed in response to the lawsuit, the Antonellis charged that Riggs had breached its duty as their financial adviser by encouraging them to "support the loans of another customer" while failing to disclose all "material facts" about those loans.

The court papers did not say who the other customer was or what information Riggs allegedly withheld. The Antonellis admitted that they had not paid the $3.7 million but denied that the money was "due and owing" to Riggs. A Riggs spokesman and a lawyer for Antonelli declined to comment on the suit.

In early August, one of Antonelli's lawyers said the 68-year-old chairman of Parking Management Inc. could be forced into bankruptcy if his lenders refused to give him time to work out his financial problems.

The lawyer, Roger Frankel, said Antonelli was asking about 50 lenders to relax repayment terms on hundreds of millions of dollars of real estate loans that were in default or appeared headed for default.

Real estate sources said Antonelli's troubles stem largely from business relationships he forged with several other developers. Antonelli guaranteed loans for real estate ventures managed chiefly by those developers but was hard pressed to fulfill his guarantees when problems arose, sources said.

Riggs is the second bank to take Antonelli to court in Washington since he became squeezed for cash. Earlier, the National Bank of Washington sued Antonelli to collect $4 million. Government regulators later seized NBW and sold its deposits to Riggs.

Both NBW and Riggs lent millions to the Antonellis based on their promise to repay rather than any specific collateral. When a borrower defaults, such unsecured creditors, as they are called, are in a position to exert considerable pressure on the borrower. They may force the borrower to sell property to raise cash, complicating the borrower's efforts to keep other creditors at bay.

Another Washington real estate investor fighting to stay out of bankruptcy, Conrad Cafritz, had $36.5 million of unsecured borrowings as of April 30, according to a report from Cafritz to his creditors.

A New York real estate brokerage company this week added to Cafritz's problems, suing him for payment of a $302,000 commission it said it is due from the expected sale of a building at 409 12th St. SW. In a letter filed with the suit, Cafritz said he has no obligation to pay the commission to Julien J. Studley Inc.