LONDON — Prime Minister Blair promised yesterday that he would stand down from his post “in the next few weeks” in a late attempt to avert a large protest vote against Labour in tomorrow’s midterm elections.

He is planning to announce next Wednesday or Thursday that he is resigning as Labour Party leader, a move that should see Gordon Brown succeed him in Downing Street by July 2.

Mr. Blair used a television interview on the 10th anniversary of the 1997 general election victory that swept him to power to confirm that he will be gone within weeks.

He later endorsed Mr. Brown as his successor, ending months of speculation over whether he wanted the chancellor to take over or would prefer another heavyweight member of the Cabinet to succeed him.

His announcement was aimed at disillusioned Labour voters, whom he fears intend to give Labour a “kicking” because they are angry with him over issues such as Iraq.

Mr. Blair’s day of carefully choreographed farewell appearances began on the GMTV sofa. “I’ll make my position clear next week, I’ll say something definitive then,” he said.

He effectively anointed Mr. Brown, saying he would make a “great prime minister” — an act of reconciliation with the chancellor after years of tension between them

Before flying to Scotland for a final campaign visit, Mr. Blair was warmly cheered during a visit to Labour’s headquarters in London.

Campaigning in Scotland, where Labour is facing a strong challenge from the pro-independence Scottish Nationalist Party, Mr. Blair said: “Within the next few weeks, I will not be prime minister of this country. It will be time for a new leadership.”

Chatting with an Edinburgh family later, he said he was “looking forward” to leaving no. 10, saying: “It’s a long time, 10 years — probably long enough for lots of other people.”

The deputy prime minister, John Prescott, has announced he will hand in his resignation as deputy Labour leader at the same time as Mr. Blair quits.

The prospect of a Cabinet-level challenge to Mr. Brown has all but disappeared but he could still face a contest with either John McDonnell or Michael Meacher from the left of the party. Approximately seven weeks after Mr. Blair resigns, an electoral college will be held, almost certainly in London, attended by delegates from unions and other affiliated organizations, constituency Labour parties, MPs, and Euro-MPs.

Union officials and other Labour Party figures are now working on the assumption that the college will be held on Saturday June 30 or Sunday July 1.

That timetable would see Mr. Blair going to Buckingham Palace formally to resign on Monday, July 2, with his successor being invited to form a government by the queen shortly afterward.

Downing Street dropped a clear hint that Mr. Blair would wait until after the resumption of devolved power in Northern Ireland next Tuesday to make an announcement about his future.

David Cameron, the Conservative Party leader, said Mr. Blair’s time as prime minister started with great hope but ended with disappointment.

He had done some good things like making the Bank of England independent but had not fulfilled his promise to save the NHS.

“Tony Blair will be remembered as a successful party leader but not as a good prime minister,” Mr. Cameron said.

Almost three-quarters of voters think there should be a General Election when Tony Blair steps down as prime minister and hands over to his successor, according to a poll for BBC 2’s Newsnight program last night.