Local officials in Alexandria and Arlington and Fairfax counties are grappling with a new state law on condominium conversions that took effect last week.

Supporters and opponents sharply disagree on the impact of the new law and expect it will be tested in the courts.

Advocates of the new law say it gives local governments more power over condo and cooperative conversions. Other observers say, however, the law is a step backward, that it greatly weakens local governments' power to use zoning laws to control conversions.

" This is one of the most regressive bills to ever come out of Richmond," said Alexandria City Council member Donald C. Casey, who opposed the bill. "It's nothing more than giving a free rein to developers. I think it will make it easier for developers to convert buildings to condominiums, and that was its specific purpose."

The law, approved by the General Assembly last winter, gives local governments the option of enacting ordinances that would require developers to aid tenants affected by conversions. But it also limits a key enforcement tool used by localities: local zoning powers.

"The bill as it finally came out of the legislature is the biggest increase in the powers of local governments to deal with condominium conversions that has ever come out of the Virginia General Assembly," said Del. John Rust (R-Fairfax), who introduced the bill in the legislature.

He acknowledges, however, that the law "prevents actions that the local governments were taking," and argues that they never had "the power or the right" to use zoning laws to deny conversions.

Aiding Rust in drafting the bill was William Thomas, a lobbyist for the Virginia Condominium Developers Association who has represented many developers before the Alexandria and Arlington councils.

Many Northern Virginia officials, who are angry about Thomas' role in the bill, say the law has all the marks of a pro-developers' bill. Thomas says, "They (local governments) have to apply a standard. . . . Frankly, I think it's the same standard the courts would make."

"This is not a pro-tenant bill, this is a pro-landlord bill," said Ira Lechner, an Arlington attorney who is the Democratic candidate for the 10th congressional district. Lechner says he fears that the law could lead to a new wave of conversions once the housing market improves.

Arlington officials, however, say the bill will improve the county's ability to regulate conversions and protect the interests of tenants. And Northern Virginia officials generally agree that new local regulations allowed by the law offer more protection to tenants facing conversions. But they say tenants would have been left high and dry if drafters of the bill had had their way.

"We wouldn't have had a provision for relocation payments if the City Council hadn't gone down and begged and pleaded with Billy Thomas," Casey said with some bitterness.

The law allows local governments to require developers of conversions to provide up to $500 in relocation payments to any tenant forced to move because of a conversion, and to reserve as many as 20 percent of units to be set aside for rental to elderly and handicapped residents for up to three years, with rents set at prevailing market rates.

In recent weeks, Alexandria and Arlington and Fairfax counties have approved ordinances setting such requirements for developers. Vienna is expected to consider similar measures later this year.

Despite the provisions for tenants, Alexandria and Fairfax officials say the law's limits on the use of zoning powers deprives them of their most powerful tool for regulating conversions.

Alexandria council member Casey says that the City Council had been able to deny conversions when developers failed to meet zoning laws. Without that power, Casey and others contend, local governments may find themselves unable to block most proposed conversions.

One of the major disputes between developers and local governments in the past has been over parking at proposed conversions.

In many cases, local officials have sought to force developers to provide more parking, often a major cost in conversion projects. Local officials say that many apartment complexes, even before conversion plans, had inadequate parking and that developers have resisted improving parking situations.

Rust admits the new law is unclear on how much parking space can be required.

Unless the parking situation will be made worse by a conversion, Rust says, local governments cannot require developers to provide additional parking. Even then, he says, it is unclear how much additional parking the developers can be required to provide.

Some local officials say they believe the law gives them the power to require adequate parking when a conversion would exacerbate parking problems, even if it means developers must remedy existing problems.

Other officials say that the entire parking question is so murky they expect the issue to wind up in the courts.

In fact, some Northern Virginia officials believe the new law is likely to spawn a host of lawsuits.

"You're really not going to know what the effect [of the bill] is until it is used and tested in the courts," said Vienna Mayor Charles H. Robinson.