(Adds postponement by SPD lawmaker)
BERLIN, June 20 (Reuters) - Germany's parliamentary budget committee will discuss paying the next tranche of aid to Greece next week, a senior lawmaker from the Social Democrat Party (SDP) said, prolonging uncertainty over whether the deal needs parliamentary approval.
Three months before an election, some lawmakers from the SPD, the junior partner in Angela Merkel's coalition, are seeking a full parliamentary debate on the 8.5 billion euro loan to Greece - which would expose sharp divisions within Merkel's conservative parliamentary group.
The budget committee, which had been expected to meet on Wednesday, has to decide if the full house has to approve the disbursement of a fresh tranche that was agreed to by euro zone finance ministers last week.
"The budget committee will only address the latest decision of the Eurogroup in its next weekly sitting," the SPD's budget policy spokesman Johannes Kahrs said.
"It is clearly uncomfortable for the (conservative) fraction that the IMF is not involved ... even though (German finance minister Wolfgang) Schaeuble promised it would be."
The IMF has said it would like to see some of Greece's debts being written off in return for its participation in the bail-out deal, a move that would be unpopular in Germany.
Earlier, Merkel ally Michael Grosse-Broemer had said that no parliamentary vote would be needed, suggesting that the budget committee could nod the new deal through.
Some of Merkel's own conservatives have in the past opposed aid to Greece. Sixty-three of the 309 members of her conservative parliamentary group voted against the third bailout for Greece in August 2015. There were three abstentions.
Schaeuble has said a full debate on the credit lifeline in the lower house could lead to market uncertainty. (Reporting by Markus Wacket, additional reporting by Thomas Escritt; Writing by Madeline Chambers; Editing by Alison Williams and Pritha Sarkar)