The same mail last week brought press releases from the National Association of Letter Carriers and the National Taxpayers Union, both rejecting the recommendations of the bipartisan National Commission on Social Security Reform.

The postal workers and their allies in the federal employee unions warned that their 6 million active and retired members, who now have their own retirement system, would fight anyone who tried to force them to join Social Security. The taxpayers' group, claiming a membership of 100,000, said it would fight because "it's time to draw the line on tax increases."

Normally, that kind of cross fire from large organized interest groups would be enough to shatter an uneasy consensus. Instead, the prospect is that a solid majority of both parties in Congress and the president will, in the words of Sen. Alan Simpson, "agree to lock arms and go over the cliff together," in support of something resembling the commission's package.

The breakthrough scored by the commission headed by Republican economist Alan Greenspan could be the harbinger of other deals. According to several commission members, that last-minute agreement reflected more than Greenspan's negotiating skills and the willingness of both the president and House Speaker Tip O'Neill to encourage a compromise. It represented a stark fear of the implications of failure.

"How many more disasters can we afford?" was the rhetorical question of one commission member, Sen. Daniel P. Moynihan. Failure, he said, would have sent out a message that, even when faced with imminent financial collapse of a lifeline program for millions, the politicians lacked the self-discipline to take the difficult actions that were needed.

Moynihan now thinks "it is possible" that similar agreements can be forged on the budget, defense- strategic policy and environmental-economic growth issues. But it will not be easy and certainly not automatic, Moynihan says, given the differences of views and the institutional-political problems to be overcome. His fellow commission member, Rep. Barber B. Conable Jr., is even more skeptical. Without the imminent threat of collapse that faced Social Security, Conable says, Congress and the administration are unlikely to buckle down to the hard work of balancing defense, tax and budgetary claims.

"I don't think the 98th Congress will be that much different from the 97th," Conable says, meaning that posturing and partisanship may again dominate.

History and experience are on Conable's side of the argument. But I have a hunch that the atmosphere has changed in ways not yet fully appreciated by the veterans of many years of political wars. The brutal reality of our situation is forcing everyone away from doctrinal rigidity and into a search for action. Stalemate is intolerable in times as serious as these.

You could see that in the statement issued last week by six former Cabinet members (of both parties) and a host of other businessmen. They appealed to the president and Congress "to display true leadership in the spirit of national unity." You could see it in the sense of concern expressed by legislators of both parties at the retirement plans of Senate Majority Leader Howard H. Baker Jr., a seeker of consensus, exhausted by the petty infighting of the last Congress.

That psychology--if it lasts--can make this an unusual and productive period in our government.