Yedioth Ahronoth said on Friday that in private conversations, Barak said the idea of reaching a peace deal with the Palestinians anytime soon was a "fantasy".
He also said that Israel would not withdraw from the West Bank before finding a solution to Palestinian rocket attacks, "which will take between three to five years".
Barak said he would not approve the removal of roadblocks from the West Bank, despite assurances given this week by Israeli Prime Minister Ehud Olmert to Palestinian President Mahmoud Abbas that some of the hundreds of checkpoints would be removed.
Olmert's meetings with Abbas would not lead to a final peace accord, the defense minister said.
"What will determine the situation in the end is if Abu Mazen (Abbas) and (Palestinian Prime Minister) Salam Fayyad are capable of implementing anything in the West Bank," Barak was quoted as saying.
Barak, whose Labour party is a leading partner in Olmert's coalition, said he did not intend to break away from the government, but said that Olmert would appear "detached from reality" when the peace talks broke down.
During a Labor Party faction meeting on Friday, Barak said, "There has been no change in my stance regarding the Palestinians. We have the responsibility of strengthening Palestinian President Abu Mazen (Mahmoud Abbas) and Prime Minister Salam Fayyad. We will do everything to make things easier for the Palestinian."
The defense minister added, "We are interested in a peace process and the American conference, but we are still being realistic. Our first responsibility is to the citizens of Israel."
As prime minister he ended Israel's 22-year military occupation of southern Lebanon without achieving a peace deal, a move applauded at the time but which later set the stage for Israel's 2006 war with Hizbullah.
Attila Somfalvi contributed to this report