A federal appeals court, reversing an Alexandria district judge's decision in a major drug case, has sharply tightened the reins on U.S. prosecutors seeking grand jury evidence from lawyers whose clients are targets of criminal probes.

The decision by a three-judge panel of the U.S. 4th Circuit Court of Appeals in Richmond means U.S. prosecutors in eastern Virginia must now prove the relevance and need for such information before grand jury subpoenas against defense attorneys will be enforced.

The ruling also sets a strong precedent for future cases in the four other states--North and South Carolina, Maryland and West Virginia--of the 4th Circuit.

Assistant U.S. Attorney William Otis, criticizing the decision, said yesterday that the court's finding "creates the potential for a good deal of delay in the grand jury's work. We do not take it lightly." He said federal prosecutors have asked permission from the U.S. solicitor general to appeal the decision to the full appellate court.

Alexandria prosecutors had sought files and records of lawyers J. Flowers Mark and William B. Moffitt. The records show expenses incurred in representing Leon Durwood Harvey of Fairfax County. Harvey, twice convicted on drug charges, is a target of a federal grand jury probe into how proceeds from Harvey's alleged drug dealing were spent.

A request by Mark and Moffitt last November to quash the subpoena was denied by District Judge Oren R. Lewis, who rejected arguments that the subpoena violated confidential attorney-client relationships and Harvey's Sixth Amendment right to choose his own attorney.

In granting the appeal, the appellate court said U.S. prosecutors had "consistently refused to reveal any details regarding the purpose of the grand jury investigation," leaving the court "unable to discern" whether disclosure of the documents might unfairly incriminate Harvey.

The decision, written by Judge Samuel J. Ervin and joined in by Judge James Sprouse, rejected a government request that the appeal be denied and the case returned to Lewis. Judge Francis D. Murnaghan dissented.

"Unless Lewis knows more than we do about the government's purposes for seeking the documents, he would be in no better position to rule on the privilege issue . . . ," the court said.

The court said it was adopting a rule established in 1973 in the 3rd Circuit that prosecutors be required to show that the documents sought are relevant, needed and not intended for any other purpose than the current grand jury probe. The ruling applies only to subpoenas against lawyers whose clients are targets of a grand jury, the decision emphasized.