The D.C. Court of Appeals ruled yesterday that D.C. attorneys who leave government posts for private practice may not engage in activities that are "substantially related" to their former work.

Lawyers said the ruling, the first test here of new court rules for members of the D.C. Bar, could reopen debate over legal ethics governing lawyers who trade government jobs for private ones. Others, however, said it was too early to tell what effect the ruling might have.

The three-member appeals panel yesterday ordered the D.C. Board of Zoning Adjustment to reconsider its decision on a conflict of interest complaint filed against two attorneys who left the D.C. Corporation Counsel's office to work for a law firm representing a builder whose construction plans they had previously contested on behalf of the city.

The complaint was filed by an opponent of the building project. The dispute centered on whether the attorneys were involved in the same matters while representing different sides. The board had ruled that no conflict could be found.

But the court, interpreting conflict of interest rules it implemented last year, drew a fine distinction yesterday, saying that conflicts can arise in matters not necessarily identical but including similar elements.

"Commonality of facts, principles, and parties legally renders these proceedings substantially related" and therefore improper for lawyers, the court wrote. But the judges said they could not make a final ruling on this specific case because the zoning board had not completely examined the facts, and they sent the case back to the board for reconsideration.

In a lengthy dissent, appeals court Judge John M. Ferren called the opinion "standardless" and "indecipherable." He said it raises the possibility that a wide range of government lawyers who are members of the D.C. bar could be barred from practicing their specialties when they return to private life.

Retired Judge George R. Gallagher, who wrote the majority opinion, said Ferren's dissent "pays lip service" to the ethics rule and consigns it "to the ash-heap."

An attorney for the two lawyers involved, C. Francis Murphy and Iverson Mitchell, now employed at the Washington firm of Wilkes & Artis, declined to comment.

Charles Buffon, vice chairman of the D.C. Bar's Legal Ethics Committee, said he expects the ruling will have only limited impact because lawyers "would give a very narrow reading" to the court's use of the words "substantially related."

While at working for the city, Murphy and Mitchell had reviewed zoning proposals submitted by builder Oliver T. Carr for a commercial and residential complex near 26th Street and Pennsylvania Avenue NW. Carr's proposals mainly concerned the availability of parking spaces.

The complaint against the two lawyers cited the fact that the law firm sought additional parking spaces for the project both before and after Murphy and Mitchell changed jobs.

The court sent the case back to the zoning board to decide the extent to which Murphy and Mitchell were involved in the case while they worked for the city.

If they were involved then, the court ruled, then they must be disqualified from participating further. Also the law firm must be disqualified, the court said, because it failed to screen the attorneys' involvement before they joined the firm.