The Nuclear Regulatory Commission has tentatively decided to suspend the operating license of the embattled Diablo Canyon nuclear power plant in California because of a series of blunders there that cast doubt on its management, regulatory sources said yesterday.

The five-member NRC is expected to vote today on the language of the suspension, which would cancel the plant's two-month-old permit for fuel loading and low-power operations until remedial action has been taken and an independent commission verifies such action.

Four of the commissioners are reported to favor the action.

The decision is a major victory for citizens' groups, members of Congress and state officials who have argued for years that the $2.3 billion plant should not be allowed to operate.

The decision also is an apparent NRC response to charges from members of Congress that failure to act would destroy NRC credibility as a watchdog over nuclear power, particularly in light of the Reagan administration push for speedier atomic plant licensing.

The Diablo Canyon plant, owned by the Pacific Gas and Electric Co., has been under attack constantly since construction began in 1977 by citizens worried about an ancient earthquake fault running under the plant's coastal site near San Luis Obispo.

Nearly 1,600 demonstrators who tried to shut down the plant were arrested in September and October, and several administrative appeals and court petitions to close it are pending.

The plant owners shut it down Sept. 28 after one of their inspectors found that drawings used to label certain crucial pipes in the plant's Unit One as safe from earthquakes actually were drawings of the pipes in Unit Two. That meant the Unit One pipes had to be checked and approved as strong enough to meet NRC requirements.

NRC Commissioner Peter A. Bradford described the pipe problem as "a major screwup" at the time, but it meant only a delay in proceeding to full power production.

However, more problems arose during the checks and other evaluations. Gov. Edmund G. (Jerry) Brown Jr. outlined 13 of them Nov. 7 in a letter to the NRC demanding the independent review. Although those errors did not make the plant unsafe, one NRC source said, "the issue is what they were symptomatic of, the entire quality assurance program."

The errors, verified at the NRC, included misapplication of specifications giving stress levels along the Hosgri earthquake fault line, use of outdated criteria for strength of supports for cables and cable holders, use of incorrect pipe weight figures and several errors in design and calculation of the range in which some structures are safe.

Together, an NRC source said, the picture emerged of "a track record of carelessness" that could not be ignored.

Under the decision taken at a closed NRC session Monday, PG&E must call in an independent consulting firm to review all of its specifications and verify that they are correct before the suspended license is restored. Such a review could take months.

A PG&E spokesman said there would be no comment until a formal announcement is made.

In a letter to the NRC last week endorsing Brown's call for the audit, Reps. John D. Dingell (D-Mich.) and Richard L. Ottinger (D-N.Y.) said that "failure of the commission to either revoke, suspend or minimally add restrictive amendments to the existing low-power test license . . . strains the faith" of NRC supporters.

Sen. Alan Cranston (D-Calif.) also wrote, saying the reported errors "shake the confidence of even the most neutral observer" in NRC staff work that led to the license. The audit, he said, was "an absolute necessity if the NRC is to retain public credibility."