Israeli and Palestinian officials welcomed the choice on Tuesday.
While noting that the appointment was not official, Tzipi Livni, Israel's foreign minister, said on Tuesday that Blair was a "very well appreciated figure in Israel" while her prime minister, Ehud Olmert, called him "a true friend" of Israel and promised full co-operation if he took the job.
Salam Fayyad, the newly appointed Palestinian prime minister, welcomed Blair's likely appointment.
''We hope this appointment will speed efforts to resume the political process to achieve the establishment of a Palestinian state with East Jerusalem as its capital,'' he said.
But the Quartet struggled to finalise Blair's appointment on Tuesday and a statement was delayed until at least Wednesday by Russian foot-dragging, diplomats said.
Blair's official spokesman declined to comment on speculation that an announcement would be made at talks attended by representatives from the Quartet, which is composed of the EU, Russia, the UN and the US.
However, he hinted that Blair would turn his attention to the Middle East peace process on leaving office on Wednesday.
"The situation in the Middle East is serious and the prime minister has made clear often his view of the urgency with which the issue should be addressed," he said.
"Clearly recent events have given that situation added urgency and therefore no doubt that is what the Quartet will be considering."
David Chater, Al Jazeera's correspondent in Jerusalem, said Blair seemed set to take a position that has been largely vacant since Hamas took power in Palestinian elections last year.
He said Blair faced an especially difficult challenge in finding a solution between Israel and the Palestinians after Hamas seized control of Gaza two weeks ago.
The takeover prompted Mahmoud Abbas, the Palestinian president, to form an emergency cabinet drawn from Fatah and independent politicians, ignoring Hamas representation.
"Tony Blair is being fitted up for a job that is a very difficult one, because unlike the previous occupant of the post he faces not only a geographic split between the West Bank and Gaza but also a political one," he said.
Chater said Blair has several skills that give him an advantage for the job of Middle East envoy.
|"We hope this appointment will speed efforts to resume the political process to achieve the establishment of a Palestinian state with East Jerusalem as its capital" |
Salam Fayyad, Palestinian premier
"His micromanagement skills in finding a resolution to what was seen as an intractable situation in Northern Ireland will aid him greatly in this task," he said.
But Chater said Blair's support for the US administration's Middle East policy is considered by Arab countries as a mark against his candidacy for the post.
"The fact that Blair stood shoulder to shoulder with George Bush in the invasion of Iraq, and that in last year's Lebanon war he failed to ask for an early ceasefire, will count against him in the Arab and the Palestinian camp."
Javier Solana, the EU's foreign policy chief, is also said to be opposed to Blair's appointment.