The decision was reached after two hours of talks on Friday at the Internal Security Operations Command (Isoc) headquarters at Suan Ruen, chaired by caretaker Prime Minister Yingluck Shinawatra.
Participants agreed to maintain the ISA instead of accelerating security measures under an emergency decree, said Lt Gen Paradorn Pattanatabut, the National Security Council chief.
Police will be the main force to handle the rally by the People's Democratic Reform Committee on Jan 13, said Lt Gen Paradorn, who is an Isoc board member.
The Royal Thai Police will deploy about 3,000 officers to be assisted by 20,000 traffic police on that day, he said.
The armed forces would serve as a unit supporting the police forces, he added.
Armed forces leaders on Thursday showed reluctance to invoke an emergency decree, which would authorise the military to take over from police as the main group responsible for maintaining law and order.
The Isoc meeting also assessed the situation on Jan 13 and participants believed that pro-government red-shirts would not parade to the capital to confront the anti-government group, said Lt Gen Paradorn.
All military leaders are on the Isoc board and all joined Friday's meeting.