The D.C. voting rights amendment suffered its second setback this week when the Louisiana House Governmental Affairs Committee rejected the proposed constitutional amendment Wednesday by a vote of 11 to 4.

The California state senate rejected the amendment Tuesday by a vote of 21 to 18.

The proposal, which would give the District two senators and one or two members of the House, had been approved by the Louisiana Senate last month, by a vote of 25 to 13.

Supporters of the ratification drive here said the vote in Baton Rouge ends the drive in Louisiana at least for this year, but they are hopeful that the amendment can be brought up in California for reconsideration next week.

Since its approval by Congress in 1978, nine states have ratified the proposal, while another dozen, not including Louisiana and California, have rejected it. To become law, the amendment must be ratified by 38 states by August 1985.

Meanwhile, D.C. Mayor Marion Barry ordered the red-and-white city flag at the Municipal Center lowered to half staff for, the July 4 weekend.He took the action, Barry said, to "dramatize the absence of voting representation in the Congress," according to Alan Grip, the mayor's spokesman.

The mayor also asked that all other D.C. flags be lowered for the holiday weekend to reinforce the protest, Grip said.