Defense Secretary Leon Panetta is giving fresh backing to the Marine Corps' version of the next-generation strike plane, the F-35, a U.S. defense official said.

The F-35, which is developing variants for the Navy and the Air Force, as well as for Britain and other allies, is the Pentagon's most expensive weapons program. It also has faced schedule delays and other problems that raised doubts about its future. Ten years in, the total F-35 program cost has jumped from $233 billion to an estimated $385 billion. Recent estimates say the entire program could exceed $1 trillion over 50 years.

During a visit Friday to the Patuxent River Naval Air Station in Maryland, where the F-35 program is run, Panetta will announce that the Marines' version is no longer on what Panetta's predecessor, Robert Gates, called "probation," according to a U.S. defense official with knowledge of the decision. The official spoke on condition of anonymity in advance of the announcement.

Gates announced a year ago that if the Marines' version of the plane had not overcome its problems within two years he would attempt to cancel it. In practical terms, that threat lost its power when Gates resigned last summer.

The plane is being built by Lockheed Martin.