Sen. Paul Tsongas (D-Mass.) thought he was doing the Reagan administration a favor. As "an outspoken critic" of the Reagan foreign policy (to use his own term) and a man who had voted against the confirmation of Alexander M. Haig Jr., for Secretary of State, Tsongas thought he had an obligation to go public with his support of President Reagan's November arms-control speech. That speech offered to withhold new U.S. nuclear weapons from Europe if the Soviets would dismantle their nuclear weapons aimed at Europe.

So he came up with an idea: He would organize a group of Senate and House Democrats, "young, anti-administration people," and go to Europe over Thanksgiving to tell the left-wing parliamentarians and anti-nuclear leaders, "We have no axe to grind for the administration, but we think this is a very legitimate proposal, we support it and we think you should take it seriously."

Tsongas took the idea to Sen. Paul Laxalt (R-Nev.), who encouraged him, and then to Sen. Howard H. Baker Jr. (R-Tenn.), who called Haig to say he thought it was an offer Haig should know about.

Haig called Tsongas and said, in effect: Cool it. A Haig spokesman says that he appreciated the gesture, but "wanted to hold it in reserve," preferring for now to let the president's speech stand on its own.

Tsongas says that as far as he can tell, when Haig said cool it, he meant, forget it.