A federal judge in Alexandria has dismissed an NAACP suit against that city's school system, ruling that its decision to close two school in predominantly black neighborhoods was not racially motivated.

Spokesmen for the Alexandria chapter of the NAACP said they were surprised at the ruling but were shocked to learn for the first time yesterday that the black organization had asked to be dismissed as a plaintiff in the case.

"I didn't know anything about the request to get out, and I'm involved in the case," said George Pope, a parent of one of the 17 student plaintiffs in the suit and the chairman of the Alexandria NAACP's publicity committee.

School board officials said they were also surprised at the NAACP's request to be dropped out of the suit filed last August.

Pope said he was not aware of the request until it was granted as part of U.S. District Judge Albert V. Bryan Jr.'s opinion, made public yesterday.

Veteran civil rights lawyer S. W. Tucker, the Richmond lawyer who handled the case, said yesterday he had suggested that the NAACP drop out as a plaintiff because "we were suing in the interest of the children, and it seemed awkwared to have an adult group representing children."

That explanation, however, only added to the confusion surrounding Bryan's ruling since NAACP members said the group had long initiated discrimination sutis on behalf of children.

Ulysses Calhoun, president of the NAACP's Alexandria chapter was clearly astonished to hear his group had been eliminated as a plaintiff. But he declined comment until he could get a "clarification" from Tucker.

Meanwhile, opposing parties in the suit either took comfort from Bryan's ruling or mulled over the prospects of an appeal.

"The judge's decision speaks for itself and shows that the decision to close the schools was based on proper economic, operational and educational considerations," said Dennis Leone, administrative assistant to Alexandria School Superintendent John Bristol.

The suit had alleged that Alexandria systematically discriminated against blacks last year when it closed two elementary schools in heavily black neighborhoods. It sought to reopen the schools, two of 14 elementary schools in the city.

One of the schools, Robert E. Lee, near the Beltway and Rte. 1, was ordered closed because of declining enrollment, school officials said at a hearing last month. The other school, Cora Kelly, located in the Four Mile Run flood plain, was shut down because of chronic flooding.

According to court documents, the school population in Alexandria has declined from an enrollment of 18,000 10 years ago to a present enrollment of about 12,000.

In his opinion, Judge Bryan said school board officials considered attendance, the physical condition of the schools and desegregation busing plans when deciding which schools to close or leave open.

Bryan also said that the plaintiffs had erred in seeking to have Lyles-Crouch Elementary School closed instead of Lee under the incorrect belief that there are more white students than blacks living in the area of the Lyles-Crouch facility.

"The evidence in the case does not persuade the Court that the defendant's action of closing certain schools in fact results in blacks bearing the burden of busing more heavily than do whites, or that the board maintains a policy of terminating schools in neighborhoods where the majority of students are black," Bryan wrote.

Pope, however. said he was "shocked the court decided the way it did" and hopes the NAACP or the parents group can find a way to appeal the decision.

Prior to Bryan's ruling, the plaintiff group had offered to settle the suit out of court if the school board would agree to reopen Lee -- which Pope called "a vital school in the black community" -- and promise not to close certain schools in the future. The board declined.