WASHINGTON — President Bush hailed a new "degree of durability" in security gains in Iraq Thursday, saying it should permit him to announce further U.S. troop reductions later this year.

With the war in its sixth year and violence substantially decreased in recent weeks, Bush gave a brief and hastily arranged update on the war that focused on progress on several fronts.

He said that violence is at its lowest ebb since the spring of 2004, that forces are in their third consecutive month with lower violence levels holding steady, and that Iraqi forces are becoming increasingly capable of both fighting and securing the country.

"The progress is still reversible," Bush acknowledged. But he added, "There now appears to be a degree of durability in gains."

Looking ahead to the next recommendation on troop levels from U.S. generals in Iraq, Bush suggested its reasonable to expect "further reductions in our combat forces, as conditions permit."

His four minutes of remarks were timed to Friday's start of reduced tour lengths for U.S. troops. Starting Aug. 1, Army units heading to Iraq will serve 12-month tours rather than the 15 months that soldiers are currently deployed. That's a milestone that Bush wanted to spotlight even though it won't apply to troops now serving.

Bush said this reduction "will relieve the burden on our forces and it will make life easier for our wonderful military families."

His appearance also was timed to now broad acceptance that the mission in Iraq is starting to shift, from mainly combat to mainly training Iraqi forces, securing the Iraqi border with Iran, rebuilding the economy and battling foreign terrorists.

Still, the conflict remains a key issue in the presidential campaign. Republican nominee in waiting Sen. John McCain has repeatedly accused presumed Democratic standardbearer Barack Obama of planning a reckless withdrawal. Obama has countered that the United States never should have gone to war there in the first place.

Some 147,000 troops remain on the ground in Iraq, now that all the combat brigades sent last year as part of the so-called surge have returned home as of this month.

As an example of the gains made, Bush noted that Iraqi forces are taking the lead in a new offensive this week in the Diyala province northwest of the capital of Baghdad, considered one of the last major al-Qaida strongholds in the region.

About 50,000 U.S.-backed Iraqi military and police forces have launched a major operation against al-Qaida insurgents in parts of the province.

"This operation is Iraqi-led; our forces are playing a supporting role," Bush said. "In the months ahead, the Iraqis will continue taking the lead in more military operations across the country."

Bush somewhat improbably claimed progress on negotiations for a long-term agreement with Iraq governing the U.S. troop presence there, including everything from rules of engagement to drivers' licenses for the military. The White House's original goal was to have it completed by Thursday — the end of July. The United Nations mandate that now allows the U.S. to be in Iraq expires Dec. 31.

But the difficult talks have spawned many disputes, including over setting timelines for troop withdrawals, and the best hope now seems to be only a stopgap agreement by the end of the year. With only a few months left of the Bush administration, the government of Prime Minister Nouri al-Maliki has taken a toughened stance on its own demands.

The president's appearance showed him eager to tout progress. But he attached qualifications at every step, wary of repeating the mistake of his so-called "Mission Accomplished" speech over five years ago, in May 2003.

"We remain a nation at war," he said. "The terrorists remain dangerous and they are determined to strike our country and our allies again."