More cases than ever were filed in the D.C. Court of Appeals last year, contributing to a record number left pending at the close of 1984 and stretching to 513 days the average time it takes judges to reach a decision, according to figures released by the court yesterday.

According to Chief Judge William C. Pryor, 1,828 cases were filed last year, a 16 percent increase over the 1,580 filed in 1983.

"This surge continues a trend, over the past 10 years, of a generally rising caseload," Pryor said in a prepared statement. " . . . The critical rate of growth of appellate court activity will likely require additional finances and personnel if substantial inroads are to be made in reducing the pending caseload and time to decision."

According to Pryor, 2,100 cases were pending as of Dec. 31, 1984, an increase of 310 cases over 1983. The average number of days from the filing of a formal appeal to a decision rose 26 days, from 487 to 513, the statement said.

In comparison, the statement said, "The American Bar Association cites, as reasonable case processing standards, periods of 130 to 190 days for criminal case appeals and 150 to 210 days for civil case appeals."

The nine-member court, the District's highest, has had a vacancy since May 27, 1984, when Judge John W. Kern III retired. Despite the vacancy, decisions were reached in 1,518 cases, only 69 fewer than 1983, said Pryor. In July, the Reagan administration nominated Deputy Solicitor General Andrew L. Frey for the post but withdrew the nomination March 22 in the face of conservative opposition when it was learned Frey was a member of a group that supports abortion and gun control.

The Reagan administration has not submitted a second nomination, but the leading candidate, sources have said, is John Montague Steadman, a Georgetown University School of Law professor.