WASHINGTON, July 4 (Reuters) - U.S. President Joe Biden on Tuesday welcomed NATO's decision to extend Secretary General Jens Stoltenberg's term by a further year, opting to stick with an experienced leader as war continues to rage on the alliance's doorstep rather than try to agree on a successor.

Stoltenberg, a former prime minister of Norway, has been the transatlantic security alliance's leader since 2014 and his tenure had already been extended three previous times.

The decision means continuity at the top of NATO as its 31 members grapple with the challenge of supporting Ukraine in repelling Moscow's invasion while avoiding a direct conflict between NATO and Russian forces.

"With his steady leadership, experience, and judgment, Secretary General Stoltenberg has brought our Alliance through the most significant challenges in European security since World War II," Biden said in a statement released by the White House.

The president said the NATO alliance was currently "stronger, more united and purposeful than it has ever been."

"I look forward to continuing the work with Secretary General Stoltenberg to further strengthen the Alliance next week at the NATO Summit in Vilnius, and ahead of the 75th Anniversary NATO Summit in Washington, D.C. next year," Biden said.

Stoltenberg, 64, is widely seen across the alliance as a steady leader and patient consensus builder.

Stoltenberg in a tweet said he was honoured by the decision to extend his term to Oct. 1, 2024.

His next tasks include overseeing a transformation of NATO forces to refocus on defending against any Russian attack, after decades in which the alliance concentrated on missions beyond its borders, such as in Afghanistan and the Balkans.

He will also have to manage differences over how involved NATO should become in Asia, with the United States pushing for a greater role in countering China, while others such as France insist that NATO must maintain focus on the North Atlantic area.

(Reporting by Kanishka Singh in Washington; Editing by Mark Porter)