FORT WORTH, Texas (Reuters) - The U.S. Navy's next round of carrier testing of the Lockheed Martin Corp (>> Lockheed Martin Corporation) F-35C stealth fighter jet will include new helmets and jets fully loaded with internal weapons, a company official told Reuters.

During the tests, scheduled for the first two weeks of October, two F-35s will also test the Joint Precision Approach and Landing System (JPALS), an all-weather, GPS-guided landing system being designed by Raytheon Co (>> Raytheon Company), Lockheed's F-35 program manager, Lorraine Martin, said in an interview. She spoke after a ceremony for the rollout of the first of the 52 F-35s that Norway will buy.

Martin said the second round of testing is a milestone for the jet, which has wider wings than Air Force and Marine Corps versions, holds more fuel, and is designed to be catapulted off the deck of an aircraft carrier, and then land, using a special hook and heavy arresting gear.

"We're really pleased with the momentum that we've got with the Navy," she said. "If you talk to the Navy's aviators, they know the aircraft has incredible importance for their ability to do what they need to do from the ship around the world."

Lockheed is building three models of the supersonic jet for the U.S. military and nine other countries: Britain, Australia, Norway, Italy, Turkey, the Netherlands, Israel, Japan and South Korea. Denmark and Canada are also considering orders.

The Pentagon plans to spend $391 billion to develop and produce 2,457 planes over the next few decades.

Total procurement is now slated to reach 3,150, but could rise, Martin told reporters this week.

She said the U.S. government is providing information about the aircraft to other countries, identified by sources familiar with the program as Singapore, Belgium, Switzerland, Poland, Finland and Spain.

The U.S. Marine Corps in July became the first service to declare an initial squadron of its F-35B jets ready for combat, with the Air Force due to follow suit next August.

The U.S. Navy, which carried out the first round of at-sea testing on the USS Nimitz last November, plans to have an initial squadron of jets ready for combat by late 2018 or early 2019.

Martin said the jets' performance during the first round of carrier testing had helped build confidence in the program.

This time, one Lockheed and three government pilots will be using the jet's improved Generation-3 helmet, which is already being used for testing on land. They will fly with a full store of internal weapons and full fuel tanks to test the jet's performance at higher weights. There are no plans to fire the weapons, officials said.

U.S. defense officials said the tests would also include catapult takeoffs with after-burner power, more night approaches and landings, engine runs for maintainers and other parameters aimed at creating conditions that are more similar to combat.

They said the tests would not include a portable version of the F-35's complex, computer-based logistics system, with the data required to be relayed via communications links instead.

(Reporting by Andrea Shalal; Editing by Matthew Lewis)

By Andrea Shalal

Stocks treated in this article : Lockheed Martin Corporation, Raytheon Company