* Military seized power on May 22 after months of turmoil
* Military wants broad political, economic reform before election (Recasts with more from briefing, martial law remains in force)
By Panarat Thepgumpanat and Kaweewit Kaewjinda
BANGKOK, July 23 (Reuters) - Thailand's junta chief could stay in charge of the country as head of a provisional government until elections are held some time next year, a legal adviser said on Wednesday, outlining details of an interim constitution.
A member of the ruling council added that martial law, imposed two days before the army seized power on May 22, would remain in force for the foreseeable future.
The military, under army chief General Prayuth Chan-ocha, said it acted to restore order after months of political turmoil as protesters tried to topple the government of former Prime Minister Yingluck Shinawatra.
Yingluck was forced to step down on May 7 after being found guilty of abuse of power by the Constitutional Court. The remainder of her cabinet was ousted in the coup two weeks later.
The military tore up the old constitution. A provisional charter was endorsed by head of state King Bhumibol Adulyadej on Tuesday, allowing the appointment of a parliament, the National Legislative Assembly, which will nominate a new prime minister.
Asked at a news conference whether Prayuth would continue as leader of the country under the interim charter, Wissanu Krea-ngam, a legal adviser to the junta, said: "The constitution allows it, but whether he is appointed or not is down to the National Legislative Assembly."
General Paiboon Koomchaya, in charge of legal affairs for the junta, suggested Prayuth could do the job perfectly.
"I don't see he has any flaws in performing his duties. As of now he is already performing the duties of a prime minister. For the past two months, he has been sitting at the head of the table at every meeting and the administration of the country has gone smoothly during these two months," Paiboon said.
The upheaval is the latest chapter in almost a decade of conflict pitting Thailand's royalist establishment and Bangkok's middle class against Yingluck's brother, former premier Thaksin Shinawatra, and his supporters among the poor.
Thaksin's devoted following in the rural north and northeast has ensured that he or parties loyal to him have won every election since 2001. He was toppled in an earlier coup, in 2006.
The military will remain in charge of national security alongside the incoming provisional government and Paiboon said martial law, imposed on May 20, would remain in force.
"It is still necessary for the peace and safety of our country," he said.
The interim constitution has provisions for a committee to draft a new, permanent constitution. It is unclear if that will be put to a referendum.
Another body, a national reform council, will have a broad remit to draw up political and economic reforms, including the reshaping of national and local government, education, energy policy and other matters.
The protesters who undermined Yingluck's government during months of street rallies - and whose leadership is close to the royalist and military establishment - wanted the electoral system to be redrawn to eliminate the influence of Thaksin.
Prayuth has said a new general election could be held late next year. Junta adviser Wissanu said the interim constitution would probably be in force for around a year, after which a new constitution would come in and elections would be held under its provisions. (Additional reporting by Pairat Temphairojana; Writing by Alan Raybould)