Fairfax Board Chairman John F. Herrity renewed his attack yesterday on the county Redevelopment and Housing Authority's decision to hire a prestigious Washington law firm and won support for a report on how much the county agencies spend on outside lawyers.

The board by a 7-to-1 vote endorsed a Herrity resolution requesting detailed legal spending figures from all county agencies and authorities. Supervisor Audrey Moore, an Annandale Democrat, opposed the measure and Supervisor James M. Scott, a Providence District Democrat, was absent.

Once the spending figures are available, Herrity said he will seek to get the housing authority's full-time lawyer, whose salary is paid in part by the county, to work directly through the county's legal staff rather than directly for the authority. "It's about time that we took some control of the housing authority," Herrity said.

The board chairman, a Republican who has long complained about the independence of some county agencies, first raised questions about the legal spending last month when the authority retained the law firm of Covington & Burling to prepare a lawsuit against Housing and Urban Development Secretary Samuel R. Pierce Jr. over the agency's failure to release funds for a controversial public housing project in western Fairfax. Pierce released $2.4 million for the 44-town house project on O'Day Drive near Centreville a week ago after the agency threatened to sue.

Herrity said yesterday that preparations for the lawsuit were unnecessary because federal officials had no choice but to release the funds.

Several supervisors defended the housing agency, charging that Herrity's complaints about the legal fees masked his general opposition to the town house project. "I don't think the legal fees were excessive," said Vice Chairman Martha Pennino, a Democrat who represents the Centreville area. "The chairman is trying to make the housing authority's job more difficult instead of easier."

"How long could we afford to have something at a standstill when construction costs are rising so fast?" Deirdre Coyne, a spokeswoman for the authority, asked. "We were asking HUD to hold up their end of the deal."

The board received a memo yesterday showing that the housing authority spent $16,000 in the last two years on outside legal fees for the O'Day Drive project. That figure included $2,500 paid to Covington & Burling in partial payment for its work last month.

The housing authority also disclosed that it spent $230,000 in legal fees in fiscal 1982, a figure Herrity termed "rather astronomical." Other board members agreed that the figure seemed high.

The authority, whose funding does not come primarily from the county, has its own attorney, Myra Barron, whose salary is paid half by the authority and half by the county. The agency maintains that she alone cannot handle its legal workload.