Even as projections of the federal budget surplus were revised upward once again, the Bush administration squared off with Democrats today over whether the government can afford everything the new president promised during the campaign, from a big tax cut to a national missile defense system.

Despite growing concern about an economic downturn that could put a crimp on tax revenues this year, the Congressional Budget Office informed members of Congress late today that it expects the surplus to swell to $5.610 trillion over the next decade, in line with estimates that have been circulating on Capitol Hill for weeks.

The new projection, which is to be released officially on Wednesday, is $1 trillion higher than the budget office's previous estimate, in July, and about $600 billion more than the Clinton administration's final projection, which was released last month.

Of the total projected surplus of $5.610 trillion, $2.488 trillion would come from the Social Security system, the budget office said, and by agreement of the two parties will be off limits for tax cuts or additional spending. The remainder, $3.122 trillion over the next 10 years, is up for grabs as Congress awaits the administration's budget proposal and begins developing tax and spending plans of its own.