Prince George's County has filed suit against the Washington Suburban Transit District, alleging that the organization is unlawfully withholding $5.5 million that should have been paid to Metro on July 1.

The suit, filed Tuesday in Prince George's Circuit Court, asks that the WSTD be ordered to release the money owed to Metro.

WSTD receives funds from the state Department of Transportation for quarterly payments to Metro on behalf of Prince George's and Montgomery counties.

Prince George's associate county attorney Steven Gilbert said yesterday that WSTD commissioners withheld both counties' July payment to Metro because the commissioners have not reached an agreement on what amount each county will get credit for.

In previous years, Montgomery County has received credit for proportionately more money as a "rebate" for operating its "Ride-On" bus service.

But this year's formula for the subisidy has not been worked out, WSTD officials said yesterday.

After the WSTD commissioners withheld the July payment to Metro, the two counties paid Metro with their own funds, based on last year's formula, according to Gloria B. Fischer, executive secretary for the WSTD commission.

The suit by Prince George's County seeks reimbursement from the commission of those funds.

Gilbert argued that the WSTB should have paid the bill on time--to avoid any possible additional charges to the counties--and worked the details out later.

Edmond Rovner, an aide to Montgomery County Executive Charles Gilchrist, said yesterday that he did not understand the suit and that it seemed ludicrous that the matter could not be worked out between Gilchrist and Prince George's Executive Parris N. Glendening.

"We were taken aback upon learning of the suit," said Fischer, who is named in the lawsuit along with Richard Castaldi, a commissioner and Prince George's County Council member, and Lanny Davis, who represents Montgomery County on the WSTD. Castaldi is also chairman of the Metro board. A hearing is set for Monday in the case.