* White House communications director Patrick J. Buchanan, without seeking Regan's advance approval, launched a one-man campaign Monday to rally support behind the president and Lt. Col. Oliver North, the NSC official who was fired because he allegedly masterminded the scheme to divert Iranian arms money to the contras. Initially, Speakes distanced Reagan from Buchanan's remarks, which included attacks on Republican critics of the president and a moral defense of possible illegal actions by North. But on Wednesday, Speakes gave formal White House blessings to Buchanan's crusade.

'NORMAL SCHEDULE'

Regan's close assistants insist that the scandal has had no impact on White House operations. "He is working a normal schedule and seeing the president frequently as he normally does. Nothing has changed, " said one aide.

Administration officials involved with domestic policy concur, noting that preparation of a new federal budget next month is proceeding on schedule. But in nearly every other area, the White House machinery seems geared to deal exclusively with the Iran-contra affair.

Rep. Dante Fascell, D-Fla., chairman of the House Foreign Affairs Committee, which is investigating the scandal, said the White House is so "preoccupied" by the Iran affair that no one is dealing with issues ranging from nuclear arms control to the budget deficit. Reagan "must provide reassurance the government is running, " he added.

In the meantime, Reagan is trying to project an image of normalcy; he even went through with the annual Christmas Party this week for the very press corps he repeatedly has blamed for stirring up the crisis in the first place.

But Reagan does have cause to celebrate the arrival of Christmas, noted one former assistant. "We're in the middle of what normally would be a month-long holiday lull, " the former aide said. "Congress is not in session, you're not getting bills coming up here every day, no one would be here if it weren't for this Iran thing . . . "