Arlington County officials, caught off guard by a report that county schools will refuse to educate neglected and delinquent D.C. foster children living in the county, were scrambling yesterday to avert a threatened lawsuit by the District government.

County Manager Larry J. Brown said he called yesterday for a report on foster facilities in the county from Martin Wasserman, Arlington's director of human services. Brown said he also expects that the county attorney will try to meet next week with D.C. officials to discuss a possible out-of-court remedy.

Noting that he has no control over the school system, which is managed by an elected board, Brown said he was surprised by Thursday's report and that he learned of it in a newspaper account.

County Attorney Charles Flinn said he is investigating the possibility that federal law requires the county to enroll the D.C. children in Arlington schools. School officials believe that state law grants them authority to choose which out-of-county pupils they will accept.

Brown and others said they don't know what prompted the school officials to implement the new policy, although some said there had been "rumors" that some of the D.C. wards in county schools had been disruptive.

One school official had written in a letter last fall that the D.C. wards were an "administrative burden" but school officials declined to elaborate on reasons for the change in policy.

County Board Vice Chairman Mary Margaret Whipple said she was concerned about the cost of educating the foster children and questioned whether Arlington was receiving more than its share of children with special educational needs.

The D.C. government pays tuition costs and up to $9,000 a year per student for special education fees, city social service officials said.

Whipple said she believes the schools' action is "not aimed at the District" but at problems within the foster care program.

D.C. officials have threatened to seek an injunction against the county schools in federal court. Brown said he expected County Attorney Flinn to try to meet next week with D.C. City Administrator Thomas Downs to discuss a possible resolution out of court.