t the urging of the chief lobbyist for condominium developers, a House committee today approved a bill that Northern Virginia officials say would strip them of the only power they have to protect tenants facing condominium conversions.

The legislation, which was introduced by Del. John Rust (R-Fairfax) but conceived and partly drafted by condominium lawyer and lobbyist William Thomas, would sharply proscribe the authority of localities to hold up zoning permits to condominium developers in order to win concessions for tenants.

In the past two weeks, the Fairfax, Arlington and Alexandria councils all have passed unanimous resolutions objecting to the bill. "It's one of the most irresponsible acts they could have done," said Fairfax Supervisor Audrey Moore. "It shows a blatant disregard for the people of moderate income and for old people."

Officials in Arlington and Alexandria were equally furious over today's 15-to-3 vote in the House Counties, Cities and Towns Committee. Alexandria Council member Donald Casey called it a "stupid bill" that was "obviously put in by somebody who's totally in the pocket of the developers or who's totally uninformed about the issue."

Said Arlington Council member John Milliken: "They've chopped the heart of out of any authority we might have have to deal with the social and human conseqences of conversions."

Rust, who said he has represented commercial but not residential condominium developers in his private law practice, shrugged off the storm of criticism today. He said that the bill, which is not expected to encounter major resistance when it goes to the House floor next week, is needed because Northern Virginia localities have "abused" the property rights of developers by holding up permits on a "willy-nilly, individual, ad hoc and capricious" manner.

Although the measure dealt with a series of highly technical zoning issues, the controversy over Rust's bill had revived a longstanding debate in the General Assembly over the adequacy of Virginia's 1973 condominium act, which was supposed to protect tenants from displacement.

Condominium conversions were rare when the law was enacted, but recently a wave of conversions has hit Northern Virginia. In Arlington County, for example, only 10 apartment complexes were converted between 1972 and 1978, compared with 17 that were converted in the two years following that period.

For years, Northern Virginia localites have sought to strengthen the 1973 law, which officials say is the weakest in the Washington suburban area, only to run into a wall of resistance from legislators jealously protective of any infringement on the property rights of developers.

In contrast to the District and Montgomery County, where developers must offer tenant groups the right to buy an apartment building before it converts, provide long-term, discounted leases to the elderly and handicapped and pay relocation assistance to tenants forced to move, Virginia law requires developers to do nothing more than give tenants 120-day notice before their building is converted to a condominium.

As a result, Northern Virginia localities have sought to use their zoning powers to pressure developers into granting concessions to tenants, particularly the elderly and handicapped.

The practice, which began several years ago in Alexandria, recently has spread to Fairfax, where just this week the council won an agreement from the Edward R. Carr Co., the developer-converter of the 224-unit Annandale Terrace Apartments, to provide leases at discounts to the elderly and relocation payments of up to $400 for tenants forced to move. As a lever to force these concessions, the council had held up the company's request for a "special use" exemption from standard parking requirements under the zoning code.

The prime mover behind the Rust bill was Thomas, a politically influential lobbyist for Virginia Condominium Developers Association, who has represented many developers before the Alexandria and Arlington councils.

"Bill came to me and asked me if I'd like to do it introduce the bill and I said, 'Sure,' " Rust recalled. "We sat down and wrote the language over a five-day period, with a lot of going back and forth."

Thomas, whose law firm generally is credited with writing the state's 1973 condominium law, was the only witness to testify today for Rust's bill. He said later that the bill was needed to "provide a standard" for tenants by requring local governing bodies to grant zoning permits in most cases.

"There have been plenty of cases where they've been frustrated over the zoning code," Thomas said. "It's been a problem that has been festering."

Thomas said that the bill was not prompted by any particular case. One of his own clients, the Port Royal Development Corp., which is converting the 208-unit Port Royal Apartments in Alexandria, had their request for parking and height zoning permits held up by the City Council last fall because its offer to the tenants failed to measure up to city guidelines. Port Royal later made a more generous offer, including long-term leases to the elderly, and was granted the permits.

"Bill Thomas is an extremely able lawyer," Alexandria council member Casey said today. "But when he starts . . . stepping all over my constituents, I get upset."

Of the four Northern Virginia delegates on the committee, only Mary A. Marshall (D-Arlington) voted against the bill. Delegates Warren Barry (R-Fairfax) and Gladys B. Keating (D-Fairfax) joined Rust in voting for the bill.