Alexandria School Board members criticized a City Council plan for development of the 400-acre Potomac Yard site yesterday that leaves only three acres for a future elementary school.

The dispute has aggravated tensions between the council, which is focused on limiting government spending and bolstering the city's tax base, and the School Board, which is grappling with student enrollment growth and a state testing system that threatens the schools' accreditation.

"Overcrowded classrooms and unaccredited schools will have a corrosive effect on the tax base of this city," said Claire M. Eberwein, vice chairman of the School Board. "I had been more hopeful that the council would realize that requests for land at no cost for future school sites made sense from their planning perspective also."

The council's plan for development of Potomac Yard, approved Wednesday, includes a 625-room hotel, 1,900 town houses and apartments and office space.

The council rejected the School Board's request that it deed over five acres on the site for a school that may be needed as early as 2002. And the three acres that are being reserved for a school remain under the council's control.

City Council members said they shared the School Board's concern about enrollment growth but preferred to see whether school crowding continued before committing themselves to a larger school site that might not be needed.

"Enrollment is a very moving target, to say the least," said City Council member David G. Speck (D), "and before we commit both land and capital we need to have more information."

The school system has 11,000 students, and school officials project it will have 12,000 in the next six years.

A new elementary school, the first in Alexandria in decades, will open in the west end of the city next year, but board members say it will not provide nearly enough room for the anticipated growth.

Board member Mark R. Eaton noted that the request to the council was not for exclusive use of the land, but for a promise that it would be reserved as open space for recreational use until school needs became clear. "It was an effort to resolve cooperatively the issue of whether the school site would really be there when we need it," Eaton said.

Virginia law requires that each elementary school have a minimum of four acres, plus one acre for every 100 students enrolled. "If they only reserve three acres, and it turns out, as things do, that plans change and there's no adjacent open space, then we cannot have a school there," said School Board member Sally Ann Baynard.

But council members said that because development in Potomac Yard will be gradual, it will be no problem to assemble a parcel larger than three acres if school construction becomes necessary. They also said it is possible that student enrollment will fall in other parts of the city, allowing children who move into town houses and apartments at Potomac Yard to attend one of Alexandria's existing schools.

School Board member Dan Goldhaber said he does not doubt City Council members who say they will provide more space if future enrollments demand it. But without the property in hand, the board has no guarantee this will happen, he said.

"City councils change, and a promise by this council does not necessarily bind a future council," Goldhaber said. "There is no strong constituency against a school at this point, but there surely will be in the future when the land is more actively used."

Speck said of the School Board members: "If I were on their side I would probably be expressing the same discontent. But they want to put a reserve sign on that land, and that is not what we are prepared to do at this time."