Worried that an important loan-guarantee program has ground to a standstill, renewable energy industry associations sent a letter on Wednesday to President Obama urging him to speed the program along.

The signers represented virtually every type of clean energy — wind, solar, geothermal, hydro, nuclear, combined heat and power, and biomass — and reflected the industry’s concern that a loan guarantee program for clean energy projects approved in the stimulus package was stuck in the federal bureaucracy, as has been a similar loan program that predates the stimulus.

The letter, seen by Green Inc, cited “disagreements” between the Department of Energy and the Office of Management and Budget over regulations to carry out the loan guarantees. Three months have gone by since the stimulus packaged passed, the letter stated, “and we have little confidence that ongoing discussions between D.O.E. and the Office of Management and Budget over these regulations will produce a satisfactory result in a timely manner.”

“With access to these loan guarantees,” the letter continued, “our member companies will be able to start construction of planned projects that would otherwise need to be delayed or canceled due to current capital market conditions.”

Vice President Joseph Biden and the White House chief of staff, Rahm Emanuel, were sent copies of the letter, as were Energy Secretary Steven Chu; Peter Orszag, director of the Office of Management and Budget; and several other senior officials.

Renewable energy companies have suffered from the difficulties in the banking sector, which had been their primary source of financing.

The loan guarantee program has been viewed as an important tool for restarting activity in the clean energy sector. However, in four years, the Department of Energy has tentatively awarded only one loan guarantee — in March, to a solar company.

Mr. Chu has stated that the loan guarantee program is a priority, but the industries clearly remain concerned about regulatory hurdles. The letter recommends ways to speed the program forward.