AUGUSTA — A bill to make Maine the second state with a single-chamber legislature won initial approval from the House on Tuesday, but its prospects remained uncertain as it lacked the two-thirds support it needs for final passage.

The bill, approved by a 78-66 vote, would amend the state Constitution to combine the Senate and the House of Representatives. The unicameral legislature would have 151 members, who would be called senators, as they are in Nebraska, the only other state with a single-chamber system.

If approved by voters, Maine’s new body would be seated in 2016, after redistricting that’s scheduled for 2013.

The bill’s sponsor, Rep. Linda Valentino, D-Saco, said Maine’s present system was adopted during an age when slower communications and difficult travel restricted lawmakers’ access to their constituents.

“It is no longer 1820,” Valentino said, referring to the year Maine became a state.

She reminded representatives that their vote alone could not change the House-Senate system, and asked them to let voters make the final choice.

She also questioned the cost of running the 35-member Senate, saying a single chamber could govern more efficiently.

“Do the people of Maine need to continue to spend almost $11 million for a second body? Do we really need to have 28 full-time staff and seven part-time employees to staff 35 members? Do we really need to spend over $300,000 every budget cycle to support one member from the (Senate) when less than 10 percent of that $300,000 actually goes to their salary and expenses?” Valentino asked. The $11 million represents the two-year cost.

An opponent, Republican Rep. Kenneth Fredette of Newport, said a unicameral legislature would give each lawmaker more constituent work, requiring more staff assistance and expenses.

“All we will do is require more staff and more cost, and we will be giving more power to the staff,” Fredette said.

Others said passage would weaken representation of residents in rural counties, which would lose more seats than those in more urban counties.

Passage would “effectively eliminate another layer of representation,” said Rep. Bradley Moulton, R-York.

Two years ago, a similar bill drew 89 votes in support, still below the number needed to send it to voters. This time, the measure has an 8-5 vote of support from the Legislature’s State and Local Government Committee. The bill faces further House and Senate