A liberal citizens' lobby assailed the Reagan administration yesterday for an "obsession with secrecy" and said an opinion poll shows that a majority of Americans believe "the government is not open enough."

In a 142-page report, People for the American Way criticized the administration for issuing more than 280 "secret laws," increasing the Pentagon's "black budget" for secret projects to at least $22 billion, binding millions of federal employes to secrecy contracts and reversing a 30-year trend toward fewer classified documents.

The group denounced the "extraordinary power" of the Office of Management and Budget. It decried OMB's authority to decide which government publications are released, to set up information-collection policies for all federal agencies and to rewrite federal regulations.

Because of OMB's rejection of proposed regulations, "health risks have been perpetuated, the workplace has become less safe and government resources for citizens have been eliminated," the group charged.

Accompanying the report were results of poll by the Roper Organization. More than 90 percent of those surveyed said openness in government is important for good citizenship; to prevent waste, fraud and abuse, and to produce better laws. Sixty percent said they wanted their government to "aggressively work to open the flow of government information to the public."