A leading environmental think tank known for avoiding political confrontation yesterday broke with tradition and accused the Reagan administration of fostering "singleminded" policies that threaten to increase pollution and health hazards.

"The bipartisan consensus that supported federal protection of the environment for more than a decade has been broken by an administration that has given priority to deregulation, defederalization and defunding domestic programs," the Conservation Foundation said in a 439-page report released yesterday.

The sharp attack on the administration is the first of its kind by the 34-year-old nonprofit research group, known in environmentalist circles as "the Vatican of the conservation movement" for its studied avoidance of politics and confrontation.

Foundation president William K. Reilly said in an interview that the group, whose board is studded with industrialists and financiers often supportive of the president, felt it had no choice but to criticize the administration's policies. The board approved the project and while it has not yet reviewed the findings, it "was probably realistic enough" to expect a critical report, Reilly said.

Reilly said the foundation and its researchers spent more than six months and $300,000 studying environmental problems ranging from soil erosion to acid rain to wildlife extinction and found administration policies "wanting across the board."

The group sent the report to the White House last week, but a spokesman said the administration would have no comment. Interior Department officials also declined comment, but Environmental Protection Agency spokesman Byron Nelson denied the charges, saying EPA has become more efficient in what he called "a year of progress."

The foundation's attack on the Reagan record came in a report entitled "State of the Environment 1982." The report documents improvements over the last decade in controlling conventional problems such as air and water pollution, but it sounds the alarm over a new generation of threats such as toxic chemicals, acid rain, hazardous waste disposal and indoor pollution.

The threats loom larger, the report says, because of the Reagan administration's "sweeping cuts" in environmental protection programs--for example, a proposed 43 percent reduction in EPA's funds for research and development--and parallel increases in Interior and Agriculture department programs designed to speed development of natural resources. It said EPA's Superfund program has enough funds to deal with only 300 of more than 2,000 hazardous waste sites that pose serious pollution problems.

The report was most critical of cuts in programs that gather data on the impacts of pollution.

"We have no monitoring data sufficient to describe accurately the extent or developing seriousness of any environmental problem," the report says. "Hazards to public health will not be reduced simply because the federal government learns less about them."

Several activist environmental groups responded with surprise to the report, noting that the foundation has always played the role of mediator in the last decade of emotional debate between industry, politicians and conservation groups. Recently, Reilly helped Reagan aides set up behind-the-scenes dialogues with environmentalists to try to defuse the heated debate that has polarized the two sides since Reagan took office.

But Reilly said in an interview that he sees "no evidence of any substantive new directions that would warrant a change in the posture of the environmental movement." He said he hopes his group's strong stand and research-oriented approach will persuade the administration to reverse its policies. For now, the report says, those policies "allow conservationists no alternative but to protest."