LOS ANGELES — A proposal to repeal a gasoline tax increase for transportation projects in California was trailing Tuesday in early returns.

Proposition 6 had about 44 percent of the vote after polls closed Tuesday with nearly 2.9 million votes counted.

The Republican-backed measure would repeal an increase in fuel taxes and vehicle fees that is expected to fund $5 billion a year in road fixes and transit improvements over a decade. It would also require voter approval for any future gasoline tax hikes.

Republicans hoped the measure would boost GOP turnout in contested congressional and state races. They argue that California is too expensive and should spend its money more wisely to meet transportation needs.

The Legislature, led by Democrats, passed the fuel tax increase last year to generate about $52 billion for transportation funding. Opponents of the repeal, including construction industry leaders and unions, contend the funds are critical to fix aging freeways and bridges and improve transit.

Much of the money is generated through a 12 cent-per-gallon boost in gasoline excise taxes that took effect last November.

The repeal was proposed by San Diego talk radio host Carl DeMaio, who led a successful recall campaign earlier this year against a Democratic state lawmaker from Orange County who voted for the fuel tax increase.

Republicans and Democrats agree that California needs a transportation overhaul as suburban commuters clamor for freeway fixes and city dwellers demand mass transit, but they differ on where the money should come from.

Those who support the initiative argue that California ought to use existing funds for transportation improvements.

Opponents contend there aren’t enough funds to keep up with the transportation needs of California’s 40 million people. Over the past two decades, cars have become more fuel efficient — a boon for the environment but a challenge to transportation budgets as drivers need less gasoline.

Proponents argued during the campaign that the measure was assigned a misleading ballot title — “eliminates certain road repair” — that doesn’t immediately tell voters that it’s a repeal proposal.