U.S. Court of Appeals Judge Roger Robb, appointed to the court here in 1969 by President Nixon, has informally advised the Reagan administration that he plans to leave the bench.

The leading candidate to replace Robb on the prestigious 11-member appeals court is University of Chicago law professor Antonin Scalia, an outspoken conservative scholar who is widely recognized as an apostle of judicial restraint.

Scalia, who declined to comment when asked if he was under consideration for the nomination, would be the fourth well-known conservative academic named to the nation's appeals courts by the Reagan administration, which has vowed to change the direction of what it considers an activist judiciary.

Scalia would join Robert Bork, a former solicitor general and Yale Law School professor, on the appeals court in Washington. Ralph Winter, a Yale labor law professor, and Richard A. Posner, also of the University of Chicago, have taken seats on other federal appeals courts.

Administration officials would not comment on Robb's plans to leave the bench, or on the possibility that Scalia would be nominated to take his place. Several sources confirmed that those are the current plans, noting, however, that while Robb has notifed administration officials of his intention, he has not submitted a formal resignation.

Robb, 74, could not be reached for comment late yesterday. A former federal prosecutor, he was a partner in the law firm of Robb, Kisler and Parkinson before he was named to the appeals court. Robb has been considered a part of the court's conservative block.The Reagan administration is known to put particular importance on appointments to the federal appeals court here, since the bulk of the court's caseload involves the review of complex U.S. regulations often vigorously contested by private parties.

Scalia has been a coeditor of "Regulation," a publication that keeps a critical eye on government rulemaking for the American Enterprise Institute, a conservative thinktank. Scalia's area of expertise is administrative law, which deals with interpretation of federal regulations, and constitutional law. He was also a member of a Reagan campaign committee that drew up plans for federal regulatory reform.

Scalia, 45, is a graduate of Harvard Law School and served from 1974 to 1977 as assistant U.S. attorney general in the office of legal counsel.