South Korean test pilots are visiting Lockheed Martin’s F-35 plant in Fort Worth, Texas, this week after a similar trip this month to Boeing’s F-15 plant in St. Louis amid signs that Seoul will delay a decision in its $7 billion-plus fighter competition until early 2013.

Lockheed spokesman Mike Rein said South Korean officials were evaluating the F-35 Joint Strike Fighter proposal submitted by Lockheed in South Korea’s 8.3 trillion won competition for 60 new fighter planes. He gave no further details.

Seoul had expressed disappointment that its pilots would not be allowed to fly the F-35 fighter, which has only one seat. Lockheed officials said the plane was still in development, and Japanese pilots had not been allowed to fly it either during their competition last year.

Instead, South Korean pilots were being given access to a sophisticated F-35 simulator and rides in chase planes as Lockheed test pilots showed off the capabilities of the F-35 Lightning II, according to two sources familiar with the plans, who asked not to be named.

Dennis Muilenburg, chief executive of Boeing’s defense business, said the South Korean pilots went to the company’s St. Louis, Missouri, plant earlier in September to fly a prototype of a stealthy variant of the two-seat F-15 fighter plane, complete with internal weapons bays.

He said Boeing was “very confident” about its proposal, citing the capabilities of the modified F-15 warplane called the “Silent Eagle” and a proposal that would give South Korean companies a strong industrial role on the new fighter.

“They flew our airplanes extensively,” Muilenburg told Reuters at the Air Force Association conference. “We think that’s one of the advantages of the F-15. It’s available; they understand it. They have an installed fleet.”

Muilenburg said the South Korean pilots had tested the capabilities of the F-15 Silent Eagle on a number of missions.

European defense company EADS also submitted a bid in the competition, offering its Eurofighter Typhoon.