Barack Obama is to announce that the United States and the west will pour billions of dollars into the Middle East in support of Egypt, Tunisia and other countries embracing democracy, a move the White House portrayed as being on the scale of aid to former communist countries after the fall of the Berlin Wall.

Speaking in Washington, the president will attempt to reposition the US as a champion of the newly-emerging Arab democracies. His speech comes amid criticism that the US has been too slow to support the uprisings, and has adopted contradictory approaches in its dealings with different countries.

It is his most important speech on the Middle East since Cairo in 2009, when he called for a new beginning in relations between the US and the Muslim world. The support for Obama in the Arab world in 2009 has since dropped sharply.

The speech will deal mainly with the Arab spring, hailing the benefits of democracy and respect for human rights, in spite of America's long-time support for authoritarian regimes in the region.

Senior Obama administration officials, briefing on the speech, said he will take a fresh look at the Middle East after a decade of tension and division. With the winding down of the Iraq war and the death of Osama bin Laden, "we are turning a page", one official said, adding that the democracy movements reinforced this.

The official suggested that the best way to support democracy was through economic reform, and drew comparisons with the massive injection of American aid to Europe after the war, and with the support given to central and eastern Europe in 1989. The US is to relieve Egypt of up to $1bn in debt and lend or guarantee up to $1bn. The World Bank, the IMF and other multilateral institutions to provide a further $2bn-3bn. The official described Tunisia and Egypt as beacons, models to encourage others to pursue democracy.

"It is the beginning of a long-term effort," an official said. The speech is expected to last 45 minutes, a long one by Obama's standards. He is to devote a big portion to castigating countries such as Iran and Syria. The US Treasury announced sanctions on Wednesday targeted for the first time at Syria's president Bashar al-Assad over the brutal crackdown on pro-democracy protesters. Six other Syrian officials were also added to the sanctions list.

"The actions the administration has taken today send an unequivocal message to President Assad, the Syrian leadership, and regime insiders that they will be held accountable for the ongoing violence and repression in Syria," said David Cohen, the acting Treasury undersecretary for terrorism and financial intelligence. The European Union on Tuesday imposed fresh sanctions against Syria but did not include Assad.

The US assets freeze on Assad is mainly symbolic as the Syrian leader has few assets in the country but it is a sign the US has lost patience with a president it once hoped might initiate reforms.

The US is facing criticism for engaging in military action to bring down the Libyan leader, Muammar Gaddafi, but refusing to become sucked into similar action in Syria. It has also faced criticism for being slow to cut ties with traditional US allies such as the former Egyptian ruler Hosni Mubarak. The US issued only a mild rebuke over the violent suppression by another ally, Bahrain, of pro-democracy protesters.

Obama's speech comes after intensive debate within the White House between those arguing that the US should be at the forefront of the democracy movement, and those whose concern is US national security and protection of oil supplies. The few billion dollars proposed so far is not comparable to the vast sums the US sent to Europe after 1945, and some of it has already been announced by the World Bank and the IMF.

Obama will next week urge the leaders of the G8 rich countries to provide aid when he meets them at a European summit.

On Tuesday, Obama pledged several hundred millions of dollars in aid to King Abdullah of Jordan, even though that country has not been at the forefront of the democracy movement. This could raise questions about the value of the billions of dollars to Egypt and Tunisia as incentives to the democracy movement.

The White House spokesman, Jay Carney, said that the president saw a historic moment of opportunity.

"In the last decade, our focus in the region was largely on Iraq, which was a military effort, and on the hunt for Osama bin Laden and the fight against al -Qaida," Carney told reporters. "That fight against al-Qaida continues, but there is an opportunity in that region to focus on advancing our values and enhancing our security, and that's what the president looks forward to discussing in his speech."

As part of the attempt to portray the US as fully behind the reform movement, the White House yesterday released details of a call between John Brennan, a White House adviser on national security, and President Ali Abdullah Saleh of Yemen, urging him to sign a political agreement that would allow Yemen "to move forward immediately with its political transition".

Obama will also express his continued hopes for an Israeli-Palestinian peace deal. He will discuss the issue with the Israeli prime minister, Binyamin Netanyahu, at the White House tomorrow, and is to address the conference of the Israeli lobbying organisation Aipac on Sunday before leaving for Ireland and Britain.

A poll published on Tuesday by the Washington-based Pew organisation found that President Obama remains unpopular among countries polled in the Middle East and elsewhere in the Muslim world, except Indonesia.