A sharply split arbitration panel has awarded pay increases of 3.5 percent a year to more than 500 white-collar Metro employes after a bitter six-year dispute between the transit authority and the employes' union.

John N. Gentry, chairman of the three-member arbitration board, said the settlement would provide "the basis for a very, very constructive relationship" between the transit agency and union.

He described the panel's 2-to-1 decision as "fair and equitable" and added, "I've gotten some flak from both sides."

However, Thomas R. Roth, the union's representative on the arbitration board, denounced the award as "totally unresponsive," "punitive" and improper. He refused to sign the decision and said the union would consider challenging portions of the award in court.

"The two things we were looking for are cost-of-living protection for the employes and parity for employes. We got neither," said Ric Klein, a Metro systems analyst and negotiator for Local 2 of the Office and Professional Employees International Union.

Metro General Manager Carmen E. Turner praised the award as a "balanced decision" and said it would lead to "an important period of stability" for labor relations.

The dispute between Metro and the union local went to arbitration last July after negotiations on a contract broke down.

The arbitrators' award is expected to result in the first contract between Metro and Local 2, which has won the right to represent secretaries, clerks, accountants, computer specialists, lawyers, engineers, planners and other white-collar employes. Their salaries range from $10,000 to $50,000 a year.

Local 2 is the second largest union at Metro. About 5,500 bus drivers, train operators, mechanics and other workers are represented by Local 689 of the Amalgamated Transit Union.

The Local 2 award provided for a 3.5 percent pay increase retroactive to Oct. 1, a 3.5 percent raise next Oct. 1, and a 3 percent increase a year later. Metro had proposed an initial 3.5 percent raise. The union sought larger increases.