WASHINGTON (Reuters) - Government spending would plummet by nearly $6 trillion over the coming decade under a Republican plan due to be unveiled on Tuesday, in a sharp contrast to President Barack Obama's fiscal plan.

The plan, crafted by House Budget Committee Chairman Paul Ryan, envisions a total spending cut of $5.8 trillion over the coming decade, according to an aide.

That's well beyond the $4 trillion in savings envisioned by an Obama task force last year, and roughly six times the savings that Obama's own budget plan would generate.

Ryan's plan, which would take effect when the next fiscal year starts on October 1, is expected to propose sweeping changes to the Medicare and Medicaid health programs, as well as hard caps on government spending and tax cuts.

Though it is likely to win the support of the Republican-controlled House, it is not expected to get much support in the Democratic-controlled Senate.

Still, it will probably push a debate over government spending that has dominated Washington this year well into the 2012 election season, when both Obama and many of his Republican adversaries will face voters.

(Reporting by Andy Sullivan; editing by Eric Beech)