WASHINGTON — WASHINGTON -- Political momentum is always easier to recognize than it is to define, and President Clinton clearly has achieved it with his success in winning approval from the House of Representatives for his budget plan and economic stimulus package. Whether that momentum translates in the Senate is, however, another question. On the face of it, the success of a new Democratic president in passing legislation in an overwhelmingly Democratic House is something short of a political miracle. But what the votes demonstrated is that there is at least some sense of party identification among the Democrats in the House right now. The defections -- 22 on the stimulus package, only 11 on the budget -- were minor and predictable dissents from conservatives, some of them with special problems in their home districts that dictated opposition. What was more striking, and more significant politically, was the number of conservative Democrats who went along with Clinton although many of them obviously harbored doubts about the depth of the deficit reductions and the efficacy of the new spending plan. This group included many from the "Oil Patch" states -- Texas, Oklahoma and Louisiana -- in which the president's energy tax is demonstrably unpopular. The message these members were sending was that they were willing to take a political hit in the interest of supporting Clinton's attempt to get the country off dead center economically. On the stimulus package, the defections were minimal in light of the fact that so few of the Democrats are likely to realize any substantial benefit back home from the new federal spending. On the contrary, the prime beneficiaries are likely to be the old cities of the Northeast and the Midwest "Rust Belt," including those with large populations of unemployed people. The Democrats appeared to be reacting to two pressures. The first was a feeling of connection to the first Democratic White House in 12 years that dictated, as one member put it, "giving him a vote" to get started. The second was the message the electorate sent last year that Americans are sick and tired of gridlock. As Majority Leader Richard A. Gephardt put it, "I think the American people are watching tonight. I think that with all their hearts and all their minds they want us to act now." The situation in the Senate is somewhat different. For one thing, the Senate is always less responsive to the pressures of the moment because only one-third of its members are facing re-election campaigns next year. For another, there are at least 12 Democrats, most of them conservative, who are so strong at home they are almost impervious to ordinary pressures. The Democratic margin in the Senate is 57-43, and there is a strong likelihood that two or three conservative Democrats -- Sen. Richard C. Shelby of Alabama is the prime example -- are likely to oppose both parts of the plan. There are others, led by Sen. David L. Boren of Oklahoma, who want to be sure the deficit reduction is nailed down before voting for the stimulus. The one Democrat in the most awkward position is appointed Sen. Bob Krueger of Texas, who faces a May 1 primary election in which he is facing stiff Republican opposition and an electorate that, recent polls show, is clearly hostile to both the new president and energy taxes. But Clinton now has a strong argument from the House vote -- what he called "a wonderful beginning" -- to bolster his case for party unity in demonstrating that the Democrats can govern after all these years of complaining about Ronald Reagan and George Bush. Nobody on either side imagines that the Clinton program is either a quick fix for the economy or the perfect solution to the more fundamental long-term problems. As a result, there is a strong chance that parts of the program will be altered before the Senate finally approves it. But the House has demonstrated that it is possible for Congress to get off the dime and make a serious approach to domestic concerns. And the members of the Senate, loftily detached though they may be, understand that it was the failure of George Bush to project that image that cost him re-election last year. No one would be rash enough to predict that President Clinton is home free on the strength of his success in the House. But, at the least, he has picked up some momentum, however you define it.