Rajapakse, who was prime minister in the government, won the presidency by a razor-thin margin last week over former premier Ranil Wickremesinghe and on Monday named nationalist politician Ratnasiri Wickremanayake as the new prime minister.
A politician, who declined to be named, said Rajapakse faced pressure from coalition allies over cabinet posts.
"The original plan was to limit the number of ministers to 25, but given pressures from coalition partners we may have to increase it to about 30," the senior politician in the government said.
"The president has also put his foot down and rejected some demands by key political figures, but he is facing a lot of problems to accommodate all interests within the coalition."
In his campaign, the new president called for a review of the peace process with Tamil Tiger rebels.
He was expected to name the rest of the cabinet Tuesday ahead of a new session of parliament called for Friday to ratify a state of emergency in place since August 13.
The current emergency laws were declared by former president Chandrika Kumaratunga on August 13, a day after foreign minister Lakshman Kadirgamar was assassinated by suspected Tamil Tiger rebels.
Emergency laws give sweeping powers to police and security forces to arrest and detain suspects for lengthy periods without warrants. - AFP
-Amal Jayasinghe: email@example.com