A Maryland appeals court refused a request yesterday by Doctors' Hospital of Prince George's County to further postpone a lower court order that the facility reduce its rates to make up for some $21 million in patient charges that a state regulatory agency ruled were excessive.

The state Court of Special Appeals in Annapolis also denied the hospital's petition for a substantially lower appeal bond while the case is carried to the Maryland Court of Appeals, the state's highest.

In November 1983, the Maryland Hospital Cost Review Commission found that Doctors' had overcharged patients by $16.8 million. The amount grew to $21 million when the commission's order was stayed during the hospital's appeal and the old rates remained in effect.

The Lanham hospital had asked for an appeal bond of $550,000 after Baltimore Circuit Judge David Ross on Monday set a higher amount of $12.4 million, plus $1.2 million for each month the stay remains in effect.

By posting the bond, the hospital would, in effect, guarantee the amounts it allegedly overcharged should it ultimately lose its case.

On July 30, Ross upheld the commission's finding, but the hospital obtained a further stay from the Court of Special Appeals, pending Ross's setting of an appeal bond. The hospital contended Ross' ruling, if enforced, would result in its having to declare bankruptcy.

Hospital administrator Dr. Leon Levitsky, who is also a major stockholder in the for-profit facility, declined yesterday to say whether the institution would continue its appeal or institute charges mandated by the Maryland cost review commission.

"It's not a public thing, it's a private thing," Levitsky said. "I don't have anything to say."