Democrats in position to test Reagan. Iran-contra scandal, control of Congress create leverage

The 100th Congress will be the most intractable Ronald Reagan has faced as President. A confluence of personality and circumstance virtually ensures that it will be so. The Congress that convenes today makes a clean break with the three Mr. Reagan dealt with during his first six years in the White House. The 97th, 98th, and 99th Congresses were comparatively cooperative, though the legislative branch became less pliant over time.

A divided Congress - Republicans controlling the Senate, Democrats the House - ushered the ``Reagan revolution'' into place.

Now both houses are controlled by Democrats, as they were for the quarter century before the Reagan era. Fewer members than at any time in the past six years owe their political success and allegiance to Reagan. So, Congress seems ready to take its accustomed role of independence from the White House.

More than any other time in the Reagan presidency, the 100th Congress will struggle to put its stamp on an array of issues - with the cooperation of the White House or without it. With legislative initiatives on the budget and trade deficits, welfare reform, and arms control, the new Democratic majority will strive to show voters that Democrats can responsibly govern - thereby suggesting that a Democrat should occupy the White House in 1988.

The tone of the new Congress was decreed, in part, by the voters who handed the Senate back to the Democrats. Now the legislative calender in the Senate is controlled by Democrats instead of Republicans. In addition, both houses of Congress have new leaders: James C. Wright Jr. of Texas is sworn in at noon today as the new Speaker of the House; Robert C. Byrd of West Virginia, the leader of the Senate Democrats, regains the majority leadership post he relinquished to Republican leader Howard Baker in 1980.

Senator Byrd and Representative Wright, anxious to impress their colleagues as strong leaders, are giving every indication they will not back away from confrontation with the White House.

In addition, the relationship between the new Congress and the Reagan administration is certain to be affected by the extraordinary series of events that have followed the November elections. The Iran-contra scandal evoked outrage from Democrats and stunned disbelief from the President's allies in Congress.

Now Congress settles down to its business while special, Watergate-style committees in the House and Senate sift laboriously through information and testimony about the affair.

These events probably will affect congressional consideration of the President's request for an additional $105 million in aid to the contras. More worrisome to Reagan's supporters, however, is the effect that an exhaustive, and public, examination of the affair could have on the President's prestige and influence.

The limits of Reagan's political popularity were suggested to many congressional Democrats and Republicans by the thrashing Republican Senators received at the polls. The Iran-contra scandal may have imposed further limits on the President's influence, particularly if it undermines his credibility and personal popularity.

``These are the most dangerous waters the President has ever been in,'' says one senior Republican staff member in the House.

Democrats will not wait long to test the limits of presidential clout. The beginning of a new Congress is usually notable for its lack of activity. Not so this one: To meet the strictures of the Gramm-Rudman deficit reduction law, the administration released the outline of its fiscal 1988 budget request one month early yesterday. Democrats scheduled the first congressional budget hearings for today.

This week, Speaker Wright will reintroduce two bills that the President opposes. One is massive trade legislation passed by the House last year and branded by the administration as protectionist. The other is the $18-billion Clean Water Act, passed by both houses last year but vetoed by the President after Congress adjourned. He said it was too expensive.

Both houses also plan to consider several arms-control issues and a highway funding bill early in the session.

But there are dangers for the Democrats. Ronald Reagan remains popular with the public. Polls have shown a greater public willingness to let Congress have a say in foreign affairs, but that support could be squandered if the Democrat-led legislative branch is perceived as not comporting itself in a responsible manner.

At the same time, budgetary matters may put Democratic leaders in a worse bind than their Republican counterparts found themselves in last year. By law, the budget deficit is supposed to be cut to $108 billion for the next fiscal year. This year, it stands at about $175 billion. Some Democrats, including House Budget Committee chairman William H. Gray III of Pennsylvania, suggest that $135 billion might be a more reasonable target. Yet Reagan continues his opposition to increased taxes to plug the deficit, and Democrats insist that they will not propose additional taxes unless the White House does.

Thus, the Democrats may face the unpleasant choice of cutting domestic programs once again or facing charges from the Republican opposition that they are not fiscally responsible.