Ronald Reagan's pledge to cut back federal regulations may be bearing some early fruit--at least judging from a 50 percent drop in the past six months in the number of appeals from regulatory agency decisions filed in the U.S. Court of Appeals here.

Appeals from agency rulings, which ran at 69 a month a year ago, are now averaging 35 a month, according to court figures. Appeals of Environmental Protection Agency rulings alone have dropped from 18 per month to about two per month.

Judge Patricia M. Wald, who noted the sharp fall-off in a recent speech to the American Bar Association's annual Administrative Law Judges Symposium in Crystal City, called the decrease "dramatic."

Wald said the reduction might be the result of a lengthy administration moratorium last year on new regulations, or simply the result of a slowdown while the new administration settles in. In either of those cases, the fall-off would be temporary.

But another explanation could be that corporations and others regulated may now be more able to "work it out with the agency," Wald said. If that is the reason--and most observors are certain that it is--then the reduction could go on "at least for a couple more years," she said.

About half the appeals court's caseload had been administrative appeals. Recent court figures show they have dropped to about 30 percent in a court that handles about 25 percent of all agency appeals filed in federal courts.

All that spells good news to a court with a backlog of more than 1,500 cases. According to court records, the backlog is down by about 170 from a year ago.

But it also may doom the court's longstanding quest for additional judges. It had wanted to add three members to the 11-member court. The U.S. Judicial Conference agreed to ask Congress for one more. Some observers doubted Congress, especially this year, would create any new judgeships. When the newly tightfisted lawmakers take a look at this circuit's figures, the prospects look even bleaker.

Footnote on Wald: Father Time may make Wald the first woman chief judge of a U.S. Court of Appeals. Chief judges of the federal circuits are installed on the basis of seniority and must step down when they become 70 years old.

In the D.C. circuit, Judge Malcolm R. Wilkey is due to succeed Chief Judge Spottswood W. Robinson III when Robinson turns 70 in 1986. Wilkey, who is 63, would have to step down on Dec. 5, 1988.

Wald, who would be 60 years old then, would be able to serve for 10 years, which would be the longest tenure since Chief Judge David L. Bazelon's 16-year reign, which ended in 1978. It would also be a marked departure from the recent musical chairs cycle on that court, which has had three chief judges in the last four years.