The D.C. statehood convention, in a clearly political gesture to the Republican-dominated U.S. Senate, voted last night to require minority party representation on all boards and commissions in this heavily Democratic city under a proposed constitution that must pass Congress if the District is to achieve statehood.

The 45-member convention gave tentative, first-reading approval to the measure, which specifies that at least one independent or minority party member must belong to each of the more than 100 regulatory commissions and professional boards in the city.

Some panels, such as the Public Service Commission and the Board of Elections and Ethics, have only three members and would thus give a Republican or other minority party member a large voice.

Registered Democrats outnumber Republicans by about 6 to 1 in the city.

"There may be nothing more in this constitution that better enhances the chances of this document passing in Congress," said Ward 3 convention delegate Philip Schrag in urging reluctant Democrats to support the measure during last night's debate. " . . . It is a reflection of political reality."

Schrag said in an interview later that the action--taken on a voice vote--shows the "political maturity of the convention."

Convention delegates, meeting in often stormy sessions since early March have been cautioned by city political leaders to write a simple, orthodox document, something that looks "as much like systems that congressional members are accustomed to as possible," as D.C. congressional Del. Walter E. Fauntroy put it.

D.C. Republican State Chairman Robert S. Carter also has told delegates that GOP members are wary of the city's statehood bid and are waiting to see what kind of document the convention produces.

Last night's proposal for minority party representation, introduced by Ward 2 delegate Wesley Long, says: "Not all members of any board or commission shall be members of the same political party."

Several delegates and the convention's general counsel, Ralph C. Thomas III, opposed the move, saying the constitution should be free of such political details. Also, opponents said, the proposed state's governor, who would appoint the commission and board members, should have a free hand in those selections.

Concern for minority parties "does not have to be written into the constitution," argued at-large delegate Barbara Lett Simmons. It can be contained in the formal legislative history accompanying the constitution, she said.