Leterme's party emerged as the clear winners of the election on June 10, but French-speakers have resisted his key demand to devolve more powers to Belgium's regions.
The continued stalemate had prompted much speculation that the 177-year-old country would split.
"Overall, I am extremely pleased with the result," Jo Vandeurzen, the head of the Christian Democrat party, said.
The agreement came as the two chambers of parliament held their first full sittings since poll, with the outgoing government acting in a caretaker role.
Under the provisional deal, which will only come into effect if the parties form a government, non-European Union citizens will be able to come to Belgium to fill jobs when there are not enough EU candidates.
It would also prevent immigrants joining family members in Belgium unless the latter had a secure income.
Negotiators said that Belgian citizenship would only be granted to those who have spent five years uninterrupted in the country and who speak one of the three official languages - French, Dutch or German.
The groups will next meet in an attempt to find a compromise on justice issues, Leterme's spokeswoman said.
Brussels, the officially bilingual Belgian capital, lies in the middle of Dutch-speaking Flanders in the north and Francophone Wallonia in the south.
About 6.5 million Belgians speak Dutch, compared with four million French speakers.