The Department of Energy provided confidential information to the American Petroleum Institute-the industry's major trade association-before releasing it to the releasing it to the public, according to an internal investigation described yesterday by the department.

The investigation, conducted by DOE's deputy inspector general, concluded that the department "maintained a double standard of access to information that favored the American Petroleum Institute over members of the public who relied on DOE's formal procedures" for obtaining information.

The investigation report, which was sent to Energy Secretary James R. Schlesinger two weeks ago, said API "enjoyed advance access to numerous internal DOE documents (which) frequently included drafts of proposed rulemakings that would directly affect the financial interests of API's member oil companies."

"We are especially concerned about the broader implications of these findings for public confidence in the integrity of DOE's procedures for rulemaking and policy formulation" DOE Deputy Inspector General Thomas S. Williamson Jr. said in a letter with the report.

An API spokesman said last night that the institute had not had time to evalute the report but that "API cooperated fully in the investigation. An internal API investigation found no evidence of impropriety or wrong-doing."

The report, entitled "intellegence Gathering at the Department of Energy by the American Petroleum Institue," grows out of allegations last year that an API official, John Lannone, obtained improper access to DOE documents. A Ralph Nader public advocacy group. Congress Watch, publicized an internal API memo from Iannone describing his acquistion of DOE internal documents.

Iannone told superiors, for example, that his "industry comments on an advance copy . . ..were incorporated into the final draft rulemaking by DOE" on petroleum price regulations that would increase categories of costs that could be passed on to consumers without lengthy hearings.

Williamson's report indicates a conflict between Iannone's sworn testimony at Senate hearings on the subject and statements by Doe Officials during the internal investigation. DOE officials have referred the matter to the Justice Department for possible perjury charges.

"The report from the inspector general's office is a vindication of our efforts to expose DOE's continued leanings toward the oil companies and Secretary Schlesinger's lack of concern for the consumer," said Sen. Howard Metzenbaum (D-Ohio), who chaired the hearings by the Energy and Natural Resources Committee.

The report acknowledged that certain steps to end the sort of activity alleged in the study have already been taken by DOE, including a new set of regulations governing acceptance of gifts by employes. "However," Williamson said in his letter to Schlesinger, "we suggest that you expedite action on the additional measures reflected on the additional measures reflected in our recommendations for corrective action."

Among these are guiedeline for communications, "to ensure that all employes are aware of their obligation to afford all interested members of the public fair and equal access to the department's decision-making process," Williamson wrote.