It took almost all night to do it, but by 3 a.m. yesterday a bleary-eyed Alexandria City Council ended its seven-year effort to gain greater control over city development by adopting a controversial ordinance that halves the allowable density on Alexandria's industrially zoned land.

In addition to reducing density, the new law lowers the height allowed for new buildings in the city's two industrial zones, I-1, and I-2, from 150 to 77 feet, or roughly 7 stories. The measure allows developers of sites larger than 2 acres to get around the height and density restrictions and build structures as tall as 200 feet in some areas by submitting development plans subject to council approval.

Affected are about 1,400 acres, approximately 10 percent of the city's land, including a large block in the Cameron Valley area along the Capital Beltway, and the Potomac Railroads yards south of Old Town, the site of a planned massive office residential complex near National Airport called Potomac Center.

The council's action also created a new zone, M-3, for the land around the Eisenhower Avenue Metro station that will allow buildings up to 345 feet tall. That zone is designed to encourage development around the Metro site, including a skyscraper complex planned by developer Howard Hoffman.

The ordinance generally pleased development interests, including developers, landowners and their lawyers present at city hall Thursday night. Although the new law is more restrictive than the old one, the new one is viewed by these interests as reasonable and likely to encourage development.

But it disappointed dozens of representatives of Alexandria civic groups who came forward long into the night to ask for futher reductions in the density ratio, to at least half of what the ordinance eventually provided for. They objected to the possibility of tall buildings next to low-rise residential areas and to traffic such developments would generate.

Some time after midnight, Philip Sparks, the spokesman for DRIVE ON (the Daingerfield Island Voter Education Organization, a group protesting high density development on the Potomac Center site) reminded the council of a petition signed by more than 1,700 Alexandria residents in favor of lowering the density ratio.

Sparks also told the council he intends to supply every person who signed the petition with the addresses and phone numbers of city council members, no matter how they voted. This tactic, widely perceived as a threat, did not endear Sparks to the council, particularly at that hour, and was seen by many as instrumental in dooming an amendment in support of the citizen's position proposed by council member James Moran.