WASHINGTON--Contrary to President Reagan's assertion that he was not swapping arms for hostages, a Senate committee report says Reagan authorized resumption of arms shipments to Iran last January with the understanding all U.S. hostages would be released, NBC News reported last night.

The report by the Senate Intelligence Committee said the president gave his approval in January 1986 with the understanding that if the hostages were not released, there would be no more shipments, the network reported.

And while the report found no evidence the president knew about the diversion of money from Iran arms sales to Nicaragua's Contra rebels, it raised questions about the roles of key administration officials.

For example, the report was critical of CIA Director William Casey, saying he had been less than candid with the Intelligence Committee when he appeared before the panel last November. The report indicates Casey had been aware of the possibility of the funds diversion as early as Oct. 7, 1986, several days earlier than he had contended, NBC said.

The report doesn't establish how much money was actually diverted from the arms sales to the Contras or whether Lt. Col. Oliver L. North, the White House aide who was the purported engineer of the diversion, was acting alone or with orders from above, NBC said.

But the report portrayed former National Security Adviser Vice Adm. John M. Poindexter and North as frequently acting on their own and misleading or ignoring their White House superiors.

As for the president himself, the report drew only the conclusion that he seemed surprised when told that money had been diverted to the Contras, NBC said. The report said the committee could not prove or disprove whether Poindexter or North ever told the President that the Contras were being funded with the Iranian money.

Dan Howard, a White House spokesman, said: "The White House does not have a copy of the report and therefore it is difficult to respond to questions on its contents. It is essential that the full report be made available to the public rather than selected details. The rreport should be released immediately."

The report was obtained as probes into the affair moved forward on several fronts. Lawrence Walsh, the independent counsel, was said to be readying a grand jury investigation, and the senator who is heading a Senate investigation said his committee may question foreign leaders about the affair.