WASHINGTON — PRESIDENT Bush's upcoming trip to Asia has been recast since the original trip was postponed in late November.Mr. Bush's mission has shifted from more general diplomacy into an aggressive trade mission for promoting American exports and creating American jobs. The reasons are many and powerful. A president whose strength is his leadership in world affairs is watching American confidence in him fall along with confidence in the economy. In the past week, polls reported Bush's approval rating below 50 percent, the lowest of his presidency. The White House once again began using the term "recession" as signs of even sluggish recovery evaporated. And the Federal Reserve Board dropped its discount interest rate a full point to the lowest level in 27 years. This trip has become an opportunity to argue that the president's agility in foreign affairs matters on the home front. "The domestic importance of this mission can't be overstated," Secretary of Commerce Robert Mosbacher told White House reporters on Friday. "Remember, every billion dollars in exports means 19,000, almost 20,000, American jobs." Casting this trip to Japan, South Korea, Singapore, and Australia as a boost to the US economy, however, will be difficult. It puts the president in the delicate position of talking tough to the Japanese for domestic audiences without creating a backlash in Japan. The tough public talk, says Republican strategist Glen Bolger, "is out of character for the president. He's got to wave the bloody shirt over jobs. But he's more inclined to negotiate quietly between heads of state." Unless Bush has a dramatic confrontation with the Japanese, says Democratic consultant and political strategist Victor Kamber, "it's not going to be believable." The Democrats, many of whom want to hold their field position as the party that protects jobs against foreign competition, raised the stakes on Friday. House majority leader Richard Gephardt of Missouri introduced legislation that would require the Japanese to lower their trade surplus with the United States by 20 percent in each of the next five years. The Bush position is under attack from the right as well. Hard-line conservative Pat Buchanan is opposing Bush in Republican primaries with a campaign that puts protecting American jobs ahead of free-trade principles. For President Bush, free trade and internationalism are among his dearest principles. Mr. Buchanan's challenge has already forced Bush and Vice President Dan Quayle to make the case that, as the President told a television interviewer last week, "you can't separate foreign policy from domestic." Buchanan, in a way, is a prelude to what we face from the Democrats next fall," observes Fred Steeper, a Republican pollster who sometimes works for Bush. "So he could help us sharpen our arguments." Another event next month could potentially play against Bush and to isolationist sentiment on the left and right. Sometime next month, the Bush administration will host an international conference on aid to the former Soviet Union. Political operatives have been warning for months of the political pitfalls of sending aid to the former Union while barely agreeing to extend unemployment benefits to Americans last fall. Already, the US has extended $4 billion in loan guarantees and $165 million in direct food aid; $20 million in medical supplies has already been shipped. Holding this conference in Washington, Mr. Steeper agrees, could play into the hands of Democratic campaigners. "He's doing that because it's the right thing to do, not the politically right thing to do." Bush's Asia trip has turned into an unprecedented presidential trade mission. While European heads of governments routinely make commercial missions, the US has treated that as unpresidential business. This time, Bush is taking more than 20 prominent business executives with him, including the heads of the three major automaking companies. The only near-precedent for this in recent history was when Mr. Quayle took a similar delegation to Latin America earlier this year, notes John Yochelson, vice president for international business and economics at the Center for Strategic and International Studies here. Ed Lincoln, a specialist in economic relations with Japan at the Brookings Institution, does not recall a single summit with Japan during the Reagan years when trade was discussed at all. The business is likely to be mostly symbolic, although the Japanese may agree to some conciliation that Bush can bring home in triumph - possibly a major Japanese contribution to the superconducting supercollider project in Texas.