WASHINGTON (Reuters) - Republican U.S. House of Representatives Speaker Mike Johnson on Sunday proposed a three-month stopgap funding bill that excludes an immigration-related measure demanded by Donald Trump, as lawmakers look to avert a month-end partial government shutdown.

Johnson laid out the plan in a letter to colleagues released just eight days before the government's current $1.2 trillion in discretionary funding runs out on Sept. 30. The chamber will aim to vote on the measure on Wednesday, according to a source with knowledge of the plan.

Failure to act by then would furlough thousands of federal workers and shut down a wide swath of government operations weeks before the Nov. 5 election.

The proposal, which excludes a Trump demand to impose new requirements that people provide proof of citizenship to register to vote, is aligned with what Democratic Senate Majority Leader Chuck Schumer had urged, a basic extension of government funding to December. It runs through Dec. 20.

"As history has taught and current polling affirms, shutting the government down less than 40 days from a fateful election would be an act of political malpractice," Johnson said in the letter.

The House, which Republicans control by a narrow 220-211 margin, on Wednesday rejected Johnson's prior proposal for a six-month funding extension including the voter-registration measure, which Democrats and democracy advocates call unnecessary as it is already illegal for non-citizens to vote in federal elections.

Congress faces an even more critical deadline on Jan. 1, by which time lawmakers will have to raise the nation's debt ceiling or risk defaulting on more than $35 trillion in federal government debt.