BAGHDAD (AP) _ Democratic presidential candidate Barack Obama began Monday his first on-the-ground inspection of Iraq since launching his bid for the White House, with U.S. commanders ready to brief him on progress in a war he long opposed and Iraqi leaders wanting more details of his proposals for troop withdrawals.

His planned stops in Baghdad — and other areas of the country — marked the second major leg of a war zone tour that opened in Afghanistan. The contrasts in tone and message were distinct.

Obama sees the battle against the resurgent Taliban and al-Qaida in Afghanistan as America's most crucial fight and supports expanding troop strength to counter a sharp rise in attacks.

But Obama had stood against the Iraq invasion and now worries that an open-ended U.S. combat mission will sap military resources and focus — at a time when Iraq violence has dropped to its lowest level in four years.

The Illinois senator — traveling in a congressional delegation with Sens. Jack Reed, D-R.I., and Chuck Hagel, R-Neb. — arrived in the country early Monday. Their first stop was Basra, according to a U.S. official who spoke on condition of anonymity because he was not authorized to give details of the trip.

Basra is the center for about 4,000 British troops involved mostly in training Iraqi forces. An Iraqi-led offensive begun in March reclaimed control of most of the city from Shiite militia believed linked to Iran.

Obama's travel precise travel plans were kept secret, but he was expected for a meeting Monday in Baghdad — where the airport is located near the vast Camp Victory, a nerve center for the U.S. military in the palaces and gardens that were once part of Saddam Hussein's presidential compound.

The lawmakers made no public statements.

The meetings were expected to include the top U.S. commander in Iraq, Gen. David Petraeus, and other military chiefs outlining the significant gains in recent months against both Shiite militia and Sunni insurgents including al-Qaida in Iraq.

The White House and military leaders — and many residents of Baghdad — trace the momentum back to last year's buildup of more than 30,000 troops in areas around Iraq's capital. Obama's challenger, Sen. John McCain, has tried to hammer Obama on his critical remarks before the so-called "surge."

All five surge brigades have left Iraq, but there are still about 147,000 U.S. soldiers in Iraq, more than in early 2007.

Obama has endorsed removing U.S. combat forces over a 16-month period, but has been less precise on the size and type of U.S. military role needed in Iraq after an exit from the battlefield.

Iraqi leaders are expected to press Obama for more clarity on his long-term vision. Such discussions have added importance since Iraq and U.S. negotiators appear stalled in efforts to reach a long-range pact to define future U.S. military presence and obligations.

American diplomats hoped to reach a final accord by the end of the month, but it now seems the goal is a stopgap "bridge" document that would maintain the status for U.S. forces once a U.N. mandate on their presence expires at the end of the year. Such as move would leave the hard bargaining to the next president.

Iraqi leaders, meanwhile, have gained a new measure of self assurance with revenue from record high oil prices and Iraqi-led successes to hobble Shiite militias believed linked to Iran. Recently, Iraqi leaders have increasing pressure for some kind of timetable for U.S. troop withdrawals.