By David Morgan

WASHINGTON, July 18 (Reuters) - Republicans in the U.S. House of Representatives took a first step toward tax reform on Tuesday, with the release of a fiscal 2018 budget plan that would allow a tax reform package to pass the U.S. Congress without support from Democrats.

The $4 trillion blueprint, which must be approved by both the House and Senate, would also set the stage for a Republican-only repeal of the 2010 Dodd-Frank Wall Street reform law and $203 billion in savings from mandatory federal programs including food stamps over the next decade.

The plan aims to move the U.S. fiscal position from a $472 billion deficit in 2018 to a $9 billion budget surplus in 2027. The change is based in part on a committee forecast of 2.6 percent annual U.S. economic growth that assumes future changes in tax, healthcare and financial laws, as well as deregulation.

The nonpartisan Congressional Budget Office has forecast economic growth of 1.9 percent from 2017 to 2027.

Covering the year beginning Oct. 1, the budget plan represents the latest Republican attempt to show they can govern since the party took control of both the White House and Congress in January. But the cloud of party infighting already hangs over those prospects.

The House and Senate are still struggling to enact legislation to dismantle and replace Obamacare and have not yet addressed other priorities including spending legislation for 2018 or a measure to raise the federal debt limit.

The House budget plan would spend $621.5 billion on defense and $511 billion on nondefense discretionary spending in 2018.

The House Budget Committee is expected to approve the plan later this week and send it to the floor of the chamber for a full vote. But conservative lawmakers are already balking over mandatory cuts they think are too small and demanding to see a tax reform plan before supporting the measure.

The plan is vital to Republican aims of overhauling the U.S. tax code while avoiding a Democratic filibuster in the Senate.

The plan requires the tax-writing House Ways and Means Committee to find $52 billion in savings, a directive that allows Republicans to pass a tax bill with a simple majority in the Senate, which they control by a 52-48 seat margin. Without reconciliation, tax reform would require 60 Senate votes.

A $14 billion savings instruction for the House Financial Services Committee would allow the same procedure for legislation to replace Dodd-Frank, which passed the House in June. (Reporting by David Morgan; Editing by Sandra Maler)