WASHINGTON — Sen. Jack Reed, who opposed President Bush’s plan to send more U.S. forces to Iraq a year ago, said yesterday that the troop surge — in tandem with political shifts that weakened the Iraqi insurgency from within — has significantly reduced violence and visibly restored commerce, freedom of movement and other aspects of day-to-day life in the battle-torn nation.

But as he finished his 11th wartime tour of Iraq, Reed said that an “ineffectual” Iraqi government has thus far failed to sufficiently exploit the lull achieved by the “superb” performance of the U.S.-led military coalition and its partners in the Iraqi security forces.

If the central government cannot make better progress on the political element of the counterinsurgency, Reed said, the improved situation in Iraq “is fragile and could be reversed” in the coming months.

“We’ve bought time and political space” for the central government to maneuver, said Reed, describing an Iraq now free of “that sense almost of anarchy that prevailed last year.” But “if those successes do not materialize into political decisions leading to a stable Iraq,” he said, “there could be consequences that will be unfortunate for Iraq and for us.” He spoke in a phone interview from Kuwait on the first leg of a return from a trip that began Wednesday.

Democrat Reed, a member of the Senate Armed Services Committee, stressed that hard tests lie ahead as U.S. forces return to the level — under 130,000 — maintained before Mr. Bush ordered the surge at the urging of military leaders, including the commander of the U.S. coalition force, Gen. David Petraeus.

In particular, Reed said the Iraqi government needs a consensus deal on how to share the country’s oil wealth in a way that reconciles its competing ethnic and religious groups. The government also faces decisions about how to handle the demands of two powerful groups — the Kurds in the north and a segment of Iraq’s Shiite Muslim majority in the south — for virtual autonomy in their respective, oil-rich regions.

While revising his earlier view of the surge strategy — too small and too gradual to work, he said when Mr. Bush proposed it last January — Reed said he stands by his prescription for the path ahead in Iraq: a U.S. declaration of policy that fixes a date to begin reducing U.S. forces in Iraq and shifts their mission from combat to counterterrorism, and the training and support of Iraqi troops. With Sen. Carl Levin, D-Mich., the chairman of the Armed Services panel, Reed has proposed legislation to that effect for more than a year, usually with a nonbinding goal of accomplishing the mission shift by a certain date, and without fixing the size of the U.S. force to remain in Iraq. The Democratic-controlled Congress could not muster the votes last year to override Mr. Bush’s veto of such legislation.

Among his stops, Reed met in Baghdad with Petraeus and U.S. Ambassador Ryan Crocker and visited with two Rhode Island units in or near the capital city: C Battery, 1st Battalion, of the 103rd Field Artillery Brigade and the 169th Military Police Company of the Rhode Island National Guard in Ramadi. He also visited Rhode Islanders who are public-affairs specialists serving with the 65th Press Camp.

In accounting for the improved military situation since his last visit, in July 2007, Reed cited four factors — each connected to some potential liability:

•The surge in U.S. forces and their “aggressive posture,” especially in and around Baghdad. Reed said a question in the coming months will be how well the U.S. coalition force and the Iraqi army and national police are able to sustain the reduction in roadside bombings and other attacks. Reed has long argued that the surge was risky because it was a one-shot deal — impossible to sustain because of the rotation schedule of an Army already stretched thin.

•The so-called “Anbar Awakening,” the decision of Sunni Muslim tribal leaders, mostly in the western province of Anbar, to scrap their alliance of convenience with al-Qaida. Reed said Sunni leaders won’t necessarily keep backing the Iraqi government if they get no political return — such as an oil-revenue-sharing plan.

•The decision of a Shiite militia leader, Muqtada al-Sadr, to pull his forces out of the hostilities. Here as well, Reed said, Sadr’s faction could return to violent opposition if displeased with political progress.

•Diminished support for the insurgency by Shia groups tied to Iran. Reed portrayed this as a cold-blooded decision, based on Tehran’s assessment of its interests, that could be reversed.

jmulligan@belo-dc.com