By David Ingram

WASHINGTON, Nov 30 (Reuters) - The conservative U.S. federal judge who helped to appoint Kenneth Starr as an independent counsel to investigate President Bill Clinton, prompting first lady Hillary Clinton to complain of a "vast right-wing conspiracy," is planning a partial retirement in February.

The decision by Judge David Sentelle, an anchor of the conservative side of the federal judiciary, will open a fourth vacancy on a Washington, D.C., appeals court considered second in influence to the U.S. Supreme Court.

His semi-retirement, known as "senior status," was disclosed on a judiciary website that monitors future vacancies.

President Barack Obama has faced difficulty persuading the Senate to confirm his nominees for the 11-judge U.S. Court of Appeals for the District of Columbia Circuit, which hears many cases arising from federal agencies.

Sentelle, who turns 70 next year, was a federal prosecutor and judge in North Carolina before President Ronald Reagan appointed him to the appeals court in 1987.

He was chief of a three-judge panel that in 1994 appointed Starr - a former appeals court judge - as the one to investigate President Bill Clinton over a real estate investment and other matters.

Starr's investigation widened to include Clinton's relationship with White House intern Monica Lewinsky, and led to Clinton's impeachment by the House of Representatives.

Without mentioning Sentelle's name, Hillary Clinton noted the judge's ties to Republican senators in a 1998 national television interview in which she spoke about a conspiracy against her husband.

Starr released a statement calling her comments "nonsense."

Known for direct, colorful questions to lawyers, Sentelle wrote a book, "Judge Dave and the Rainbow People," based on his handling of a court case involving a gathering of hippies in the North Carolina mountains.

He did not immediately return a call to his chambers on Friday.