Despite determined opposition from Old Town residents, the Alexandria Planning Commission recommended last night approval of plans for construction of a four-story, 100-unit condominium complex on the city's southern Potomac River waterfront.

The Planning Commission voted 5 to 2 for the project on the east side of Union Street between Wolfe and Wilkes streets, just north of the old Ford plant. The site is owned by Dominion Lands, a company affiliated with Virginia Power, and is used as a parking lot. The plan was submitted by Lawrence E. Brandt, an Alexandria builder who has contracted to buy the site from Dominion Lands.

The commission's recommendation goes to the City Council.

Residents near the parcel bitterly criticized the condominium, saying it would dwarf the town house-style residences that are common in Old Town and create a bad precedent for future waterfront development.

"We oppose Mr. Brandt's plan generally for its density and its massiveness," said Ann Keith, a nearby resident. "It is inappropriate for the neighborhood . . . . "

Brandt said he would do everything he could to make the project more esthetically pleasing to neighbors, but did not offer to scale down its size. Brandt's plans comply with the zoning and height ordinances governing the neighborhood.

Several Planning Commission members who voted in favor of the proposal said they did not like it, but had no legal alternative.

"We just don't have the authority to turn these things down unless we find them unconscionable," said Commissioner Allan Kamerow. "And I don't find this unconscionable. It meets the law."

Mitchell L. Griffin, one of the commissioners who opposed the project, prompted applause from the audience when he said, "The law has been met. But sometimes you have to take a stand . . . and I think these things stink."

The Planning Commission also recommended approval of a second site plan for the same parcel that would allow Dominion Lands to build a four-story complex, including 88 residences and 46,000 square feet of offices. But Howard Middleton, an attorney for Dominion Lands, said that Dominion has agreed to sell the land to Brandt, and that the mixed-use complex would be built only if Brandt's project should fall through.