WASHINGTON Cap-and-trade legislation aimed at reducing greenhouse gas emissions appears to be dead in the U.S. Senate for the time being, but the U.S. Environmental Protection Agency continues to move forward with its own plan for regulating greenhouse gases.

USEPA Administrator Lisa Jackson has outlined her agencys plans, which originally were to have been implemented this year, in a letter responding to several senators from coal-producing states.

In their letter, the senators requested a moratorium on EPA plans to propose two rules that would regulate greenhouse gas emissions, primarily from large sources such as power plants and oil refineries.

"I share your goals of ensuring economic recovery at this critical time and of addressing greenhouse gas emissions in sensible ways that are consistent with the call for comprehensive energy and climate legislation," Jackson wrote.

Starting next year, USEPA plans to require large stationary emitters filing permit applications to address ways they will reduce greenhouse gas emissions, Jackson said. Small emitters will not be phased in until 2016.

The USEPA has not said how the agency intends to require heavy commercial vehicles to curb their emissions of carbon dioxide, but a report on the agencys website projects a rule could be proposed as early as this summer.

The National Highway Traffic Safety Administration also is to consider a greenhouse gas emissions rule later this year but first is awaiting recommendations of a diesel fuel-efficiency study by the National Academy of Sciences.

At the same time, opposition to cap-and-trade legislation and EPA rules aimed at limiting carbon emissions is growing.

Many in the commercial vehicle industry oppose such measures because they say it would cause a spike in diesel fuel prices as oil producers pass higher costs to end-users.

At least 16 separate petitions have been filed in federal appeals court seeking to overturn the agencys December finding that CO2 emissions endanger public health, a required step for the agency before it issues and enforces climate change rules.

Lawsuits or congressional action could stall the EPAs greenhouse gas emissions rulemaking efforts.

Also, a disapproval resolution that Sen. Lisa Murkowski, R-Alaska, introduced in January is expected to be voted on by the Senate. It seeks to strip EPA of its authority to regulate greenhouse gases.

Meanwhile, supporters of climate-change legislation have lost their momentum to competing issues, including the economy remaining on the skids and plenty of pressure opposing the measures.

Those developments add to a growing consensus that the cap-and-trade bill, which passed narrowly in the House last June but has languished in the Senate, wont pass this year.

Still, while the issue isnt going forward, its not going away. And, as always, Congress remains unpredictable.