By H. JOSEF HEBERT

The Associated Press

WASHINGTON – Federal scientists have been pressured to play down global warming, advocacy groups testified Tuesday at the Democrats’ first investigative hearing since taking control of Congress.

The hearing focused on allegations that the White House for years has micromanaged the government’s climate programs and has closely controlled what scientists have been allowed to tell the public.

“It appears there may have been an orchestrated campaign to mislead the public about climate change,” said Rep. Henry Waxman, D-Calif. Waxman is chairman of the Oversight and Government Reform Committee and a critic of the Bush administration’s environmental policies, including its views on climate.

Climate change also was a leading topic in the Senate, where presidential contenders for 2008 lined up at a hearing called by Sen. Barbara Boxer. They expounded – and at times tried to outdo each other – on why they believed Congress must act to reduce heat-trapping “greenhouse” gases.

“This is a problem whose time has come,” Sen. Hillary Rodham Clinton, D-N.Y., proclaimed.

“This is an issue over the years whose time has come,” echoed Sen. John McCain, R-Ariz.

Sen. Barack Obama, D-Ill., said, “We will look back at today and say this was the moment we took a stand.”

At the House hearing, two private advocacy groups produced a survey of 279 government climate scientists showing that many of them say they have been subjected to political pressure aimed at downplaying the climate threat. Their complaints ranged from a challenge to using the phrase “global warming” to raising uncertainty on issues on which most scientists basically agree, to keeping scientists from talking to the media.

The survey and separate interviews with scientists “has brought to light numerous ways in which U.S. federal climate science has been filtered, suppressed and manipulated in the last five years,” Francesca Grifo, a senior scientist at the Union of Concerned Scientists, told the committee.

Grifo’s group, along with the Government Accountability Project, which helps whistle-blowers, produced the report.

Associated Press writer Erica Werner contributed to this report.