By Lawrence Hurley

WASHINGTON (Reuters) - President Barack Obama's new plan to ease the threat of deportation for 4.7 million undocumented immigrants violates the U.S. Constitution, a federal judge found on Tuesday, handing down the first legal ruling against the plan.

The ruling has no immediate impact, with the government saying there was no reason for Judge Arthur Schwab of the Western District of Pennsylvania to address the issue in the case, which concerns 42-year-old Honduran immigrant Elionardo Juarez-Escobar.

Schwab is the first judge to rule on the legality of the plan Obama announced on Nov. 20. The executive action by the Democratic president is opposed by Republicans and is already subject to other legal challenges.

Schwab ruled that the executive action violated the U.S. Constitution's guarantee of separation of powers and the separate "take care clause," which requires the president to faithfully execute laws passed by Congress.

Schwab says he ruled on the executive action issue because he concluded that Juarez-Escobar could be eligible for relief under the executive action.

Government lawyers told Schwab that Juarez-Escobar, who has pleaded guilty to re-entering the country, was not eligible because Obama's order does not affect criminal proceedings.

(Editing by Kevin Drawbaugh and Lisa Von Ahn)