Legislation that would extend tax credits for investment in wind, solar and other renewable power for a year may pass the U.S. Senate today, but it's not clear whether it can become law.

A vote on the legislation will mark the fourth attempt this congressional session to extend the tax credits.

"What this would do is renew current law and provide for renewable energy without raising taxes at the same time," said Don Stewart, spokesman for Sen. Mitch McConnell, R-Ky.

Both Colorado senators support the extension.

Sen. Wayne Allard, R-Colo., noted his state "is a leader in the emerging renewable-energy sector."

Previous attempts to pass the extension failed when House Democrats funded them by removing tax subsidies for oil and gas companies. Senate Republicans refused to go along with that. Allard has opposed the legislation when it was tied to the oil and gas tax-benefit repeal.

Senate Majority Leader Harry Reid, D-Nev., backs the measure.

But the House Democratic leadership is concerned the Senate measure doesn't include any means of paying for the extended tax credits. House Democrats pledged at the start of this term not to pass legislation that called for spending without including a payment means.

A one-year extension of the tax credits would cost about $6 billion over 10 years. Legislation passed by the House was more expansive and expensive. The Senate has rejected that legislation repeatedly.

Extending the tax credits is necessary to keep a flow of cash into renewable energy, said Anna Aurilio, director of the Washington office for Environment America, a federation of state environmental groups.

When the tax credits have expired in the past, Aurilio said, there has been a sharp drop in investments in wind energy.