Once again, a summit of the world's richest countries opened amid angry protests and sporadic violence, as demonstrators barricaded roads and tangled with police Wednesday near the Scottish resort of Gleneagles, where President Bush arrived to meet with fellow leaders from the Group of Eight major industrialized nations.

But for all the tumult, many activists here acknowledge that considerable progress on their key demands was made in advance of the summit, in particular canceling the debt of poor nations and increasing aid to Africa. As a result, many leading antipoverty campaigners are striking a hopeful stance and now exhorting the G-8 countries to back up their pledges with concrete action.

"We're getting close to a real breakthrough, but we're not there yet -- we've got to go that extra mile," said Jamie Drummond, executive director of DATA, a group co-founded by the rock star Bono that advocates boosting support for Africa. He was speaking in an interview after attending meetings at which Bono and fellow Irish musician Bob Geldof made their case to Bush, British Prime Minister Tony Blair, German Chancellor Gerhard Schroeder and Canadian Prime Minister Paul Martin.

"Expectations are high on the basis you have a doable plan," said Geldof, who organized Saturday's Live 8 concerts in 10 major cities around the world. The concerts aimed to mobilize global opinion behind an antipoverty campaign.

"If it doesn't happen here with this group of leaders, with the personal commitment of the British prime minister, it won't happen."

Fueling such optimism are actions by G-8 countries in recent days and weeks, partly in anticipation of the popular support generated by the campaign led by Bono and Geldof. The movement has been joined by other celebrities, as well as religious groups.

European Union countries promised in May to increase their overall aid spending to 0.7 percent of national income by 2015, a target long sought by aid advocates. It would increase annual European assistance by about $26 billion in five years from current levels of about $51 billion.

That was followed in June by an agreement among wealthy countries' finance ministers to wipe out debts owed by 18 nations, mostly in Africa, to the World Bank and International Monetary Fund. And last week, Bush proposed doubling U.S. aid to Africa by 2010, which would raise the figure to more than $6 billion.

By sealing those agreements with explicit targets and dates and perhaps adding a bit more money, Drummond said, the summit could meet many of the most important goals sought by Blair, who has effectively joined forces with Bono and Geldof.

The Commission for Africa that the British prime minister established recommended doubling aid to Africa, to about $50 billion, and canceling the debts of certain African nations. He has also sought a doubling of aid to the developing world at large to about $100 billion.

The debt agreement helped defuse some of the pressure. At a meeting in Edinburgh of American activists Wednesday, actor George Clooney hailed the debt write-off as "already banked" and said the groups the activists represent deserve credit "for something you've been working on for a long time."

"Are we where we want to be? No, nowhere near," Clooney added. "But we're excited that there's movement."

There are plenty of loopholes and pitfalls in the recent promises, aid experts emphasize. Some financially strapped European governments have warned that their future administrations may be unable to meet aid targets. Furthermore, the debt accord applies only to 18 nations, not every poor country, and it requires the beneficiaries to meet economic performance standards that many activists say are too stringent.

Bush's proposal to boost aid to Africa over the next five years includes only about $800 million beyond spending hikes that were already planned under other administrations' initiatives.

The G-8 governments' recent measures did not impress many of the thousands of protesters who thronged the streets of Edinburgh and the towns of Stirling and Auchterarder on Wednesday in a bid to make their voices heard inside Gleneagles.

Police halted a planned march on the resort after about 200 extremists smashed cars and attacked shops in the early morning hours. The authorities later relented and allowed the march to proceed a couple of hours late.

More than 150 people were arrested in various melees, and more than two dozen policemen were injured, British news media reported.

"We're protesting the fact that George Bush and Tony Blair are responsible for the deaths of 100,000 people in Iraq, the environment of the planet is in danger and 30,000 people die every day of preventable diseases," said Rory Hearne, a member of the Irish Anti-War Movement. Other protesters voiced condemnations of capitalism and the domination of the world by rich nations.

Police drag protesters from a highway near the Gleneagles resort. British news media reported that more than 150 people were arrested on the first day of the G-8 summit, although many activists said they were buoyed by progress on debt relief.