The Virginia House of Delegates approved a conflict-of-interest measure today that would shield local officials from prosecution if their dealings were sanctioned by local government lawyers.

The bill also would prohibit local governments from enacting more stringent conflict laws. If approved by the Senate and signed by Gov. Charles S. Robb, the measure apparently would negate disclosure laws in Fairfax and Arlington counties.

Fairfax, for instance, currently requires more extensive disclosures by supervisors and rezoning applicants than the state demands.

By a vote of 56 to 40, the House agreed to establish an advisory ethics panel to watch over itself, which would be appointed by its Speaker, rather than a more independent panel with authority over the entire General Assembly.

Del. Mary E. Marshall (D-Arlington) likened the proposed panel to "setting the rabbits to guard the cabbage patch."

All three provisions were attached to a comprehensive measure that Sen. Adelard L. Brault (D-Fairfax) introduced last month to strengthen and clarify the state's ethics law, intended to prevent public officials from misusing their office for private gain.

The bill now goes to a House-Senate conference, but Virginia Common Cause Director Gordon C. Morse said that the shield amendment, if it stands, will render the law "utterly meaningless."

"It's preposterous," Morse said. "You get a letter from your lawyer and you can go ahead and do what you damn well want to . . . It will encourage the worst aspects of political cronyism by granting a privilege to local officials not enjoyed by any other citizens of the state."

The shield amendment, originally introduced by Del. Owen B. Pickett (D-Virginia Beach), was approved in the House on a voice vote without debate.

Pickett said county supervisors and city council members should be able to rely on the opinions of their county or city attorney, who normally are appointed by the council or board of supervisors.

Under the bill adopted today, a supervisor who received an assurance from his attorney that an act was not illegal could not then be prosecuted even if the government lawyer misinterpreted the law, according to an assistant to Virginia Attorney General Gerald L. Baliles.

County and city attorney opinions are exempt from the state Freedom of Information Act and need not be disclosed under legislation approved last year.

The bill also was amended on the House floor, with no member objecting, to make the law uniform across the state, apparently preempting local governments that want stronger laws.

After several supervisors were indicted for zoning scandals in the 1960s, Fairfax County approved stricter disclosure requirements than the state calls for in rezoning cases, and adopted even more stringent rules before awarding a cable television franchise last year.

"It looks like those things are in jeopardy," Del. Vivian E. Watts (D-Fairfax) said after today's vote.