BANGKOK, Jan 12 (Reuters) - Thailand"s cabinet has backed a plan to buy four fighter jets starting in the next fiscal year, an air force spokesman said on Wednesday, with a budget of 13.8 billion baht ($413.67 million) set aside for the procurement. The approval follows a recent expression of interest by the air force chief, Air Chief Marshal Napadej Dhupatemiya, in procuring eight F-35 fighter jets from Lockheed Martin Corp (LMT.N) of the United States. The cabinet has agreed the budget for a four-year period starting in the 2023 fiscal year, to replace some of the country"s aging F-16 jets, air force spokesman Air Vice Marshal Prapas Sornchaidee told reporters. Thailand"s currently has 12 JAS-39 Gripen fighter jets made by Sweden"s Saab (SAABb.ST) and dozens of American F-16 and F-5 jets, some of which have been in operation since the late 1980s. Napadej last month expressed a preference for the stealthy, fifth-generation F-35 because its price had fallen since it first hit the market. The first F-35A cost $221 million in 2007 but as production quantities and know-how increased, the price fell to about $79 million as of July last year as it gained appeal and buyers in more than a dozen countries. Spokesman Prapas said the type of aircraft to buy would be decided by two committees tasked with assessing the suitability of different aircraft. ($1 = 33.3600 baht)