RONALD REAGAN asked for it. By nominating as secretary of state a man with rich and still clouded ties to the most controversial aspects of the Nixon presidency. President-elect Reagan had to know he was inviting political trouble. That he went ahead anyway suggests that he values Gen. Alexander M. Haig Jr. highly. But no one -- least of all those Republicans who beat up on some Carter national security appointees -- should be claiming now that the Democrats have no proper business grilling Gen. Haig as they see fit.

The question is how they do it. Over the holidays, it seemed that some senators were trying to make an end run around both the election returns and established access procedures, by getting a soon-to-go Democratic administration to cooperate with an even-sooner-to-go Democratic committee leadership in coughing up certain files and tapes. Such a request to "provide me" with "all [National Security Council] documents, records and other information that may be relevant to the [Foreign Relations] Committee's inquiry into Gen, Haig's nomination" was made on Dec. 18 by Sen. Claiborne Pell (D-R.I.).

But no end run was ever made. Zbigniew Brzezinski, in a somewhat ambiguous formulation firmed up by Jody Powell, suggested that the two braches "work out a practical accommodation." Sen. Pell did his part. It is not yet clear just what material will be provided, and whether from the NSC, the National Archives or assorted presidential repositories -- each poses its own procedural, security and legal hurdles. The administration has made clear, however, it is not altering its release criteria now that the Senate is in Republican hands.The proper GOP response should be to follow the Democratic example and not to block any attempt by the minority party to obtain relevant material.

There is a drawback to all this argument about access. It bolsters a feeling that there is incriminating material to be found and that, even if there is not, the Nixon connection is exactly what the Senate should concentrate on. We offer no predictions of what the files or tapes hold: let's see. But notwithstanding the importance of the Nixon connection in illuminating Gen. Haig's character and style, it is far from the only or even the most important thing the Senate should explore.

What, for instance, are the nominee's views on foreign policy, especially in regard to areas and problems remote from his experience?How does his military status and training affect his outlook on diplomacy? How does his well-advertised past deference to the "commander-in-chief" square with a Cabinet officer's obligation to give the president his best independent judgment? What does he believe to be the proper relationship between the secretary of state and Congress? We doubt any revelation concerning Gen. Haig's qualifications for office as the answers to such questions as these.