WASHINGTON (Reuters) - A top U.S. Air Force general on Tuesday urged Boeing Co to aggressively market its C-17 cargo plane to foreign countries as one strategy for keeping the production line running.

Gen. Norton Schwartz, who heads the U.S. Transportation Command, said the Department of Defense (DOD) needed 205 C-17s -- 15 more than are currently planned -- to meet its own military requirements. Boeing has delivered 171 planes to the U.S. military, out of a total of 190 on order, he said.

But foreign sales could keep the Boeing production line in Long Beach, California running even longer, he told a House Armed Services subcommittee, noting that Canada, Australia and Britain had already ordered the popular transport plane.

In addition, some Gulf countries had expressed interest in more than four additional planes and a NATO consortium was looking at buying three more, he said.

“It is absolutely clear to me that there is an appetite for these machines outside the DOD procurement profile and it requires aggressive marketing on behalf of the manufacturer to see that those opportunities are realized,” he said.

“It’s a strategy for extending the production line and it’s something that should be aggressively pursued,” he added.

Pentagon acquisition chief John Young last month said the U.S. military did not need additional C-17 transport planes beyond those it has already ordered, despite an Air Force “dream list” asking Congress to fund 15 more.

He acknowledged Schwartz’s requirement of 205, but said that was not a “codified” or documented Pentagon requirement.

Congress has added 18 C-17s to the defense budget over the past two years to keep the Boeing C-17 production line rolling and safeguard jobs, despite a Pentagon decision to cap production of the popular transport plane.

The Pentagon did not include any funding for the plane in the Air Force part of its budget request for fiscal 2009, but Rep. John Murtha, a Pennsylvania Democrat and chairman of the House Appropriations Committee defense subcommittee, has already vowed to add more C-17s to the war budget for 2008.

The Air Force also included 15 C-17s at a price of $3.9 billion on an “unfunded priorities list” of weapons it says it needs but could not include in its regular budget request.

Schwartz said he did not share the view of some officials who believed future requirements, such as the need to transport vehicles being designed as part of the Army’s Future Combat Systems, would raise the number of C-17s needed beyond 205.

If money were not an issue, Schwartz said he would prefer to get more C-17s instead of putting new engines on some larger C-5 transport planes built by Lockheed Martin Corp.

But he said that option would cost “substantially” more.

Gen. Arthur Lichte, commander of Air Mobility Command, told the committee that he would like to keep the C-17 production line open and await the results of some studies underway to examine mobility and transportation requirements.

Schwartz said one study on mobility needs would be completed in January 2009, with a separate report being done by the Institute for Defense Analyses to be done in May 2009. Both would include the Army requirement as well.