The Reagan administration deserves "a failing grade" for its stance on almost every issue involving openness in government, according to the Society of Professional Journalists.

The administration "consistently took actions last year that would restrict the flow of information about the federal government to the people who pay for it," the society, which is also known as Sigma Delta Chi, protested in a statement issued yesterday by its national officers.

It said in a review of 10 issues that the steps taken by President Reagan and his administration constitute "a fundamental assault on the First Amendment."

The 28,000-member group faulted Reagan for holding fewer news conferences than any first-year president in at least 50 years and flunked his administration on virtually every other "openness in government" subject.

Included in the society's criticisms were:

Administration efforts to downgrade the Freedom of Information Act and make it easier to withhold information from the public. Many of the proposals have been incorporated in a bill approved by a Senate Judiciary subcommittee.

Administration backing of the so-called "names of agents" bill which would, for the first time, criminalize the publication of information derived from the public record. Already passed by the House, the bill could subject journalists and others to prison terms for disclosing the names of present and former CIA operatives.

Drafting of an executive order that would make it easier for government agencies to classify information as "top secret," "secret" and "confidential" and much harder for them to declassify it.

Other steps that alarmed the society ranged from CIA cutbacks on background briefings and public information to White House attempts to plug "politically inopportune news leaks" and White House claims of executive privilege as applicable to the entire "deliberative process" of the executive branch."

The only performance that won a passing grade in the journalists' view was the administration's forceful opposition to efforts by the United Nations Economic and Social Council (UNESCO) "to regulate journalists around the world and impose governmental controls on the flow of news."

The White House, in assembling its own report card on Reagan's first year as president, "wisely chose not to include his score" on open-government issues, the society said.

"During his 1980 campaign," the journalists' group concluded, "Mr. Reagan promised to 'get government off the backs of the people.' But people are hardly in a position to hold their government accountable if they are prevented from learning what it is doing."

The fight over the Freedom of Information Act is expected to resume shortly in the Senate Judiciary Committee. Proposals to make it easier to withhold information have had relatively smooth sailing there thus far, but a wide variety of organizations, including the AFL-CIO, is mounting a campaign to prevent any major changes.