WASHINGTON — The top American military commander in Iraq, seeking to reassure those concerned about the completed withdrawal of U.S. combat units, expressed confidence Sunday in Iraqi security forces and said the 50,000 American troops will remain in Iraq in a mentoring role with the capability of resuming battle operations if necessary.

Army Gen. Ray T. Odierno said it would take something like a “complete failure of the security forces” for the U.S. to step back into combat mode in Iraq.

“But we don’t see that happening,” he said during an interview broadcast Sunday on CNN’s “State of the Union.” “They’ve been doing so well for so long now that we really believe we’re beyond that point.”

His comments come amid a groundswell of worries among Iraqis and others about the stability of the country in the wake of the final pullout of U.S. combat brigades last week, especially with continued insurgent attacks and the inability by Iraqi political leaders to select a new national government following an inconclusive March election.

More than seven years after leading an invasion of Iraq, the U.S. military will officially change its function on Sept. 1 to one of advising, training and assisting Iraqi forces. The number of U.S. troops in Iraq is already down to 52,000, from more than 165,000 at the height of a 2007 surge. By the end of this month, that number will drop to 50,000 troops, who will remain until the end of next year.

On Sunday, a senior White House official said President Barack Obama will deliver a major speech on Iraq following his 10-day vacation in Martha’s Vineyard.

In the address, Obama will discuss the withdrawal of U.S. combat forces and the administration’s plans to continue the troop drawdown.

Last week, Obama made a passing mention of the withdrawal during a couple of fundraising speeches, noting that he was fulfilling a campaign promise in seeing that the combat mission in that country ended by month’s end.

Obama is due to leave the island on Aug. 29 and fly to New Orleans to mark the fifth anniversary of Hurricane Katrina. He will then return to Washington, D.C.

Gen. Odierno said Sunday that Iraqi forces were ready to provide an adequate level of internal security, despite criticisms of recent failures to protect citizens against attacks — such as the suicide bombing at an army recruitment center in central Baghdad last week that killed 48 people, for which al-Qaida has claimed responsibility.

“There’s still terrorism that is occurring here, but I will tell you that the country is moving forward,” he said. “It is moving forward along every line. It’s moving forward a little bit economically. Its security forces are improving. Its diplomatic efforts are improving. Its governmental functions are improving.”

Some analysts said the key question about the readiness of Iraqi security forces will come at the end of next year when the remaining 50,000 U.S. troops are slated to leave.

Odierno said that, in his view, the Iraqis would be ready for that transition, but others remained skeptical. Among them was Zalmay Khalilzad, former U.S. ambassador to Afghanistan and Iraq, who on Sunday called that “a tall order” for Iraq.

“The politics is extremely important now,” he told CNN” s “State of the Union.” “And this government formation is very important. This has the potential to repolarize the situation in Iraq. ... If politics doesn’t go well, if the Iraqis don’t come together to form a government ... the security gains we have made could be put at risk.”

After delays, Iraqi elections took place in March, but divisions over top jobs in the new government have led to a stalemate. Other analysts have raised concerns that the politicial uncertainties in Iraq have created more openings for neighboring Iran to exert its influence in Baghdad with funds and other means to promote its political agenda in Iraq and the region.

Tribune Washington Bureau writer Peter Nicholas in Vineyard Haven, Mass., contributed to this report.