President Reagan has "no recollection" of signing a presidential finding in late November 1985 that explicitly authorized a trade of arms for hostages with Iran, a senior administration official said yesterday.

Fired National Security Council aide Oliver L. North testified this week that he saw a signed copy of the finding, which had been drafted by Stanley Sporkin, who at the time was general counsel of the Central Intelligence Agency.

The finding is expected to figure in the Iran-contra investigating committees' questioning of former national security adviser John M. Poindexter next week. According to the report of the Tower special review board, Rear Adm. Poindexter had a copy of the finding.

The senior official said Reagan had been asked about it recently after news accounts raised questions about whether he had signed it, and the president responded that he had "no recollection" of doing so. Reagan later signed another finding that characterized the Iran initiative in terms of reaching out to moderate elements in Iran. If Reagan signed the earlier document, it would undercut his many assertions that he was not trading arms for American hostages being held in Lebanon.

The Tower board said in its report, "Despite some evidence to the contrary, the president appears not to have signed this finding." But the panel said the records of former CIA deputy director John McMahon showed that McMahon had been told on Dec. 5, 1985, that Reagan had signed the finding.

A signed copy of the document has never been found.

Presidential spokesman Marlin Fitzwater said yesterday, "Our position is that it never went to the president, period." He said the White House would "stick with the Tower board conclusion that they could find no evidence that it ever went to the president."

Also yesterday, Fitzwater said Reagan has decided not to comment on the Iran-contra hearings because "a lot of it is hearsay evidence" and "we should not be trying to influence" the hearings with comments on the testimony.

Fitzwater was asked repeatedly about Marine Lt. Col. North's testimony but he refused to address the substance of North's comments. For most of this week, White House officials have also barred reporters from access to Reagan in circumstances at which he could be questioned about the hearings, and Reagan said he would not comment on them.

Fitzwater did express satisfaction, however, with the North testimony on the Nicaraguan contras. "The administration is pleased that much of the story on our support for the contras and the freedom fighters in Central America is being portrayed by Col. North to audiences that are appreciative and understanding," he said.