Indonesia's president was due to start talks with potential coalition partners on Friday after early election results showed his party ahead, but not by as much as expected
The Democrat Party of President Susilo Bambang Yudhoyono, a reform-minded former general, won about a fifth of the parliamentary vote, based on a quick count from sample polling stations.
While Mr Yudhoyono, 59, is expected to win a second term in the more important presidential election on 8 July, he will have to rely on coalition partners in parliament, reducing the prospects for major economic reform.
Mr Yudhoyono's choice of ally will determine the extent to which he can improve the judiciary and the civil service as well as clamp down on endemic corruption.
His administration has delivered strong economic growth and brought relative peace and stability to the world's most populous Muslim nation, which also has sizeable religious minorities. But tackling corruption has proved far tougher.
Mr Yudhoyono could either continue with his current coalition partner Golkar or turn to one or two of the small Islamic parties instead.
The Democrats, which have led in most opinion polls, were ahead of former President Megawati Sukarnoputri's PDI-P with about 15% and Golkar with 14%, based on about 90% of the quick count vote sample by polling agency LSI.
Official results are not expected for days, but are not likely to differ greatly.
This is only the third general election since the fall of the Suharto dictatorship in 1998, after which Indonesia made the transition to democracy.