In a highly unusual step, the Securities and Exchange Commission issued a statement yesterday defending its decision not to take action against Citicorp for its failure to disclose allegations that the company manipulated foreign currency transactions to avoid foreign taxes and currency exchange controls.

Three of the five commissioners issued the "mea non culpa," with Commissioner John Evans opposing its issue and Commissioner Barbara Thomas removing herself from considering the issue. Thomas also removed herself from considering the original decision on Citicorp, for reasons that she has not stated.

The commission, in its statement, attacked the disclosure of its decision to the press as "illegal," characterized impressions created by statements in the press as "distorted" and declared itself willing to face questions and provide "a full account of its handling of the Citicorp matter before an appropriate congressional committee."

Disclosure of the decision has prompted calls for information from at least three congressional committees and has touched off a serious internal investigation within the agency to find out who leaked the report.

Reports of the SEC decision in February said that the SEC had rejected a recommendation by its enforcement staff to pursue sanctions against Citicorp, the world's largest foreign exchange trader.

According to those reports, one rationale given was an assertion by two other SEC divisions that it would be improper to hold bank officials liable for disclosure violations "based on unadjudicated illegal or improper conduct by a company's officers and directors unless there were affirmative representations as to management's honesty and integrity" in other company disclosures.

Yesterday the SEC gave several reasons for not pursuing sanctions against Citicorp, in addition to noting that, although "certain members of the enforcement staff believed that Citicorp violated" disclosure rules, the director of the division and two other divisions disagreed.

The statement also said that sanctions were not pursued because the allegations were not established adequately and that, even if they had been, "The alleged amounts for the years in question were not material to Citicorp." The statement also noted that the comptroller of the currency had concluded that no action was warranted under U.S. banking laws.

Another reason, according to the statement, is that "the law concerning disclosure of unadjudicated allegations is unclear" and a decision against Citicorp might have been reversed. The SEC also said that the case was essentially a banking or tax case and, besides, "The case was old."

Disclosure of the commission's proceedings is illegal, violating the rights and interests of private parties and inhibiting "the commission's ability to obtain essential cooperation of the private sector in its investigations and undermines the candid debate of critical issues by members of the commission and the staff necessary to well-considered decisions," the statement said.