Richard V. Waldron, who retired as a Prince George's County judge after 10 years on the bench and now collects a $21,000-a-year pension, has opened a private law practice in Riverdale in open defiance of state law.

Maryland law forbids former judges on judicial pensions from practicing law for compensation.

"It is my considered opinion," Waldron said yesterday, "that that law is unconstitutional -- and unenforceable."

He recently sent out announcements of his new law practice indentifying himself as a former judge.

Waldron, 62, who was appointed to the county District Court in 1967 by then-Gov. Spiro T. Agnew, first tried to get the law declared unconstitutional.

A Circuit Court judge ruled in his favor, saying the statute violated Waldron's constitutional right to practice law.

The Maryland Court of Appeals overrruled that decision but failed to decide the issue of constitutionality. It dismissed the case, saying Waldron sued the wrong party -- the state retirement board -- instead of the state attorney general or bar officials. The law was left intact.

Waldron, who claims to have spent $10,000 in attorneys' fees and court costs, decided against filing another suit.

"I've poured too much money into it," he said. "I'll just let them come after me."

Maryland Attorney General Stephen H. Sachs acknowledges that his office will probably have to get involved and may seek an injunction to prevent Waldron from practicing law in Maryland.

The statute in question says that a judge "who retires and accepts [a pension] may not, thereafter, engage in the practice of law for compensation." There is no criminal penalty for breaking the law, but injunctions may be sought against violators.

The attorney general's office has estimated that if the Maryland law is overturned, more than $200,000 in retirement benefits might have to be paid to retired judges currently practicing law who aren't collecting their pensions.

Waldron's office is at 6132 Baltimore Blvd., where he leases space from another firm. Waldron served as a judge until his term expired in 1977 and a judicial nominating commission failed to recommend his reappointment.

Waldron, who had a reputation as a tough-talking jurist, had been criticized for allegedly abusive courtroom conduct toward prosecutors, defense lawyers and defendants. At one point, County State's Attorney Arthur A. Marshall Jr. refused for about three weeks to send his prosecutors to Waldron's courtroom because of what he called the judge's "inappropriate demeanor" on the bench.

The head of the nominating commission cited Waldron's "temperament and disposition with attorneys" as the reasons for refusing to recommend reappointment. Sources said Waldron believed the appearance of organized opposition to his reappointment was his unwillingness to "let porosecutors run his courtroom" and his frequent disagreement with prosecutors' recommendations on rulings or sentences.

A number of Maryland judges have indicated privately that they would be pleased if Waldron takes the pension issue back to court, even if the cost is high.

"I know lots of judges who would be tickled to death to chip in," said one judge.