(Rewrites throughout with outgoing chief judge's comments)
WASHINGTON May 23 (Reuters) - The top U.S. patent court's chief judge stepped down from his leadership role on Friday, admitting he had raised questions about his judicial ethics by sending an email praising a lawyer who appears before the court.
Judge Randall Rader will remain on the U.S. Court of Appeals for the Federal Circuit, but he will be replaced as chief judge by Judge Sharon Prost at the end of May, the court said on its website.
Rader said in an open letter posted on the court website that he had "engaged in conduct that crossed lines established for the purposes of maintaining a judicial process whose integrity must remain beyond question."
On Thursday, The Wall Street Journal first reported on an email Rader sent to Edward Reines, a lawyer at law firm Weil Gotshal & Manges, praising his work. Reines represents software company Microsoft Corp and medical technology group Medtronic Inc respectively, in two cases before the court, according to the court's docket.
Rader later recused himself from the two cases as a result of his email, a move made public via court orders. His role as chief judge, which is a mainly administrative role, was due to end in 2017.
Although Rader did not mention Reines by name in Friday's letter, he wrote that he regretted sending an email that praised an attorney who had argued before the court. The email "constituted a breach of the ethical obligations not to lend the prestige of the judicial office to advance the private interests of others," Rader wrote.
Reines could not be reached for comment.
One of the cases was a patent appeal in which DataTern Inc accused Microsoft and German rival SAP AG of patent infringement. The case was decided by a three-judge panel including Rader on April 4, partially in favor of Microsoft and SAP. Rader wrote a dissenting opinion.
On May 5, the court reissued its decision, but excluded Rader's dissent, noting he had been recused from the case.
Rader also recused himself from a patent dispute between Medtronic and rival Edwards Lifesciences Corp.
The federal circuit, which has exclusive jurisdiction over patent appeals, has become increasingly important in recent years due to high-stakes litigation over technology patents.