The 4th U.S. Circuit Court of Appeals ruled yesterday that the U.S. courts cannot force Fairfax County to honor an agreement with citizens groups to upgrade roads in predominantly black neighborhoods.

The ruling said the U.S. court system lacks jurisdiction to enforce the agreement between the county and the citizens groups that was reached six years ago as the result of an out-of-court settlement of a lawsuit alleging racial discrimination. However, the appeals court said the citizens groups may now decide to proceed with their original suit.

In that suit, the Fairfax Countywide Citizens Association, three other groups and eight individuals had sued the county and the state highway commissioner claiming racial discrimination because many of the unpaved and substandard roads in the county were in predominantly black neighborhoods.

The day before the suit was scheduled for trial in U.S. District Court in Alexandria, the two aides agreed to two settlements. The first agreement required the state to upgrade six streets in black neighborhoods that were part of the state highway system.

The second agreement required the county to upgrade 76 additional roads within three years The state completed its obligation under its agreement and the county improved 25 roads.

Black residents not involved in the suit obtained an injunction preventing the county from upgrading one of the roads. At that point the County Board of Supervisors reviewed their agreement and on April 26, 1975, voted not to carry out the rest of the agreement.

The citizens groups than sued the Board of Supervisors and U.S. District Judge Oren R. Lewis ordered the county to fulfill its obligations and complete the remaining roads.

The three judges said in their opinion yesterday that U.S. courts cannot enforce the agreement because the dispute does not involve parties from different jurisdiction or a federal question.

"The settlement agreement between association and county, while serving to terminate litigation of a federal claim, was a private contract entered into after private negotiations between the parties. Both its validity and the interpretation of its terms are governed by Virginia law."

The 21-page opinion was written by Judges Harrison L. Winter, Donald S. Russell and H. Emory Widener Jr.