President Pervez Musharraf, who has few allies left in the assembly after their defeat in an election on February 18, has asked the assembly to meet on March 24, spokesman Rashid Qureshi said.
Musharraf, who came to power as a general in a coup in 1999, appears increasingly isolated, and there is speculation over how long the US ally will be able to hold onto power.
The incoming government has pledged to pass a resolution to reinstate Supreme Court judges, who Musharraf replaced in November out of fear they could rule unconstitutional his own re-election by the previous assembly.
The Pakistan People’s Party of assassinated former Prime Minister Benazir Bhutto will lead the coalition, but still is to name its candidate.
It could be a stop-gap prime minister, if Bhutto’s widower and political successor Asif Ali Zardari decides he wants the job.
Makhdoom Amin Fahim, a senior aide to Bhutto and Zardari’s deputy, had been favourite but his prospects dimmed after Sharif’s party objected to his contacts with Musharraf.
Other potential candidates include Yousaf Raza Gilani, Chaudhry Ahmed Mukhatar and Shah Mahmood Qureshi. They all hail from the central province of Punjab, whereas the PPP’s stronghold is the southern province of Sindh.