he rush by President Bush and Congress to endorse bipartisan cooperation after Sept. 11 was to be expected. The surprise is that the harmony has held up. Mr. Bush has transformed himself into a moderate, while Democrats are shelving some of their liberal agenda. At the Capitol, Alan Greenspan, chairman of the Federal Reserve and a Republican, and Robert Rubin, Bill Clinton's Treasury secretary, have been anointed the twin wise men of the economy, whose every joint appearance is treated with awe. Measures on presidential war powers, airline bailouts, aid for New York and even overall spending have been hammered out by Republicans and Democrats together. Partisan plotting is out of season. Lunching with a legislator from the other party is au courant.

This new spirit is as fragile as it is welcome, and its toughest test will come in early October, over the economic stimulus package. Democrats still want it focused on spending, Republicans on tax reductions. Hard-right Republicans like Representative Tom DeLay of Texas and Senators Don Nickles of Oklahoma and Phil Gramm of Texas are quietly seething over talk of scrapping proposed tax cuts for investors and corporations. But the White House has been virtually ignoring them and working with House Speaker Dennis Hastert, who actually listens to the anti-tax-cut pronouncements of Mr. Greenspan and Mr. Rubin.

Republicans are also upset about the way the current crisis has opened the doors to federal spending. Giving $20 billion to New York City was a jolt for many conservatives. Others fear ・correctly ・that the Democrats will try to exploit the current crisis to push such programs as federal rail subsidies, public health, job training and aid to the unemployed. (Senator Edward Kennedy has already proposed $30 billion.)

When it comes to spending, the White House has once again turned to Speaker Hastert, to the dismay of conservative Republicans. This week, after a great deal of haggling, the White House accepted a higher dollar figure than it wanted for overall domestic spending next year, including a substantial increase for education, rather than pick a fight.

For their part, the Democrats are so fearful of being portrayed by Mr. Bush as free spenders that they have insisted that any budget increases for the coming year be labeled as White House initiatives. Most Democrats acknowledge, moreover, that they will probably have to be careful about what they ask for. Some of them remember the first year of the Clinton presidency, when an economic stimulus package got so piled up with pork and well-meaning but not necessarily critical social programs that it collapsed under its own weight.

The bipartisan mood in Washington can be seen in odd gestures. After the president's speech to Congress, people noted the warm embrace shared by Mr. Bush and the Senate majority leader, Tom Daschle, and the affectionate presidential pinch on the cheek for Senator Charles Schumer of New York, compared with the cool handshake the president offered the Republican leader, Trent Lott. But the hero of the new mood has to be Mr. Hastert. In his three years as speaker, he has often seemed more concerned about Mr. DeLay's breathing down his neck than with trying to get passage of legislation with broad bipartisan support. His leadership approach has changed, and he is now telling Republicans they have no choice but to work with their colleagues across the aisle if they want to accomplish anything quickly.

Until the terrorist attacks this month, Mr. Bush also seemed to be a captive of his party's right wing. Then in short order he not only authorized a giant aid package for New York and the terrorists' victims, he also compromised with Democrats on language of the resolution backing military actions. He is listening to them, and other critics, on moderating the attorney general's request for expanded antiterrorism legislation for law enforcement. Democrats who talk to him come away impressed with what they say is the depth of his commitment to forge a new kind of government.

The new mood may not survive for long, but all legislators should now be trying to get as much done as they can while it lasts.