WASHINGTON (AP) — Pointing to growing threats and competition from Russia and China, the White House on Thursday announced ambitious plans to create the U.S. Space Force as a sixth, separate military warfighting service by 2020.

The proposal taps into the American public's long fascination with space — but with a military focus. The plan faces daunting hurdles and requires congressional approval. Military leaders and experts have questioned the wisdom of launching an expensive, bureaucratic new service branch.

Vice President Mike Pence announced the new force during a Pentagon speech, fleshing...