WASHINGTON — WASHINGTON -- When Sen. Richard Shelby of Alabama decided to vote with the Republicans against President Clinton's economic plan earlier this year, the White House sought to retaliate by depriving Shelby of small favors it bestowed on more loyal Democrats. But the result was a conspicuous rise in Shelby's popularity back home. And the lesson was not lost on other Senate Democrats -- or, for that matter, many in the House of Representatives. The result all through the spring and summer has been one small rebellion after another against the first Democratic presi dent in 12 years. The congressional Democrats also learned a lesson in the initial Senate bargaining on the economic plan. When Sen. Max Baucus of Montana and some colleagues from the West objected to a proposed increase in grazing fees on federal lands, the White House quickly removed them from the plan -- much to the astonishment of those Democrats who had expected a half a loaf at best. It is incidents like these that have provided the political context for the critical negotiations under way now on the Clinton economic plan. Democrats in both Houses have been emboldened to believe the president can be "rolled" and, more ** to the point, that there is no political equity in blind loyalty to him or their party. The result has been the spectacle of the president trying to put out one fire after another to get the votes for his package -- one day meeting with House conservatives, another with House liberals; one day trying to placate Senate conservatives on the gasoline tax, another trying to reassure moderates that the plan actually will work. Clinton's political position could not be much less auspicious as he brokers the legislation that is clearly the centerpiece of his entire program. His position in the opinion polls has continued to decline -- his approval rating in recent surveys is down close to 40 percent -- and he has yet to show the hard edge that might intimidate those who oppose him. To some degree, Clinton has been victimized by the early success of the Republicans in depicting the program as a return to the "tax and spend" days of the Great Society, a characterization that is patently nonsense. The increase in energy taxes -- the so-called Btu tax -- in the original plan from the White House would have cost middle-class tax payers about $200 a year and would have been spread over so many different items that it never would have had much direct political impact. The gasoline tax now being negotiated as a substitute is still modest in its impact on most Americans, although clearly more regressive than the original energy tax would have been. But the president allowed the Republicans to define the tax proposals as the "biggest tax increase in history" without making it clear that, although that might be true in dollar terms, most of the burden would fall on the affluent individuals and corporations that received such kind treatment from the Republicans during the Reagan years. Now Clinton is being advised to make one last appeal on 'D national television early next week before the final votes on the budget plan are held. The hope is that the president will be able to change that context and make it easier for those Democrats on the edge to stick with the president. Indeed, the president is already embarked on that campaign in one public appearance after another, one meeting after another with regional reporters and business leaders whose support he needs. And there is some evidence that his efforts may be paying at least a minimal dividend. A new opinion poll taken for the Wall Street Journal found, for example, that support for the economic plan has risen from 39 percent to 43 percent in the last month, with a corresponding decline in opposition. The survey also found voters more inclined to vote for a Democrat who supported the Clinton plan than a Republican who opposed it. In the end, however, Clinton's prospects rest far less on his ability to make a persuasive case with the public than on the feeling among Democrats that they cannot allow their president to fail in his first major test. As Rep. Mike Synar of Oklahoma put it the other day, "This is a test for the Democratic Party." But it is also a test for Bill Clinton.