WASHINGTON: US President Barack Obama's new strategy for Afghanistan faces a tough political test this week amid increasingly vocal opposition from fellow Democrats to escalating the unpopular war.

With Obama widely expected to seek more combat forces soon for the nearly eight-year-old conflict, lawmakers were due to grill the top US military official, Admiral Michael Mullen, in a public hearing on Tuesday.

Mullen, renominated to lead the US joint chiefs of staff, was to go before the Senate Armed Services Committee days after the panel's powerful chairman, Democratic Senator Carl Levin, warned against a build-up of US forces.

Levin, recently returned from Afghanistan, called Friday for redoubling efforts to train, equip and deploy Afghan security forces before any further expansion in US troops, which are set to reach 68,000 by the end of the year.

"We should increase and accelerate our efforts to support the Afghan security forces in their efforts to become self-sufficient in delivering security to their nation -- before we consider whether to increase US combat forces above the levels already planned for the next few months," said Levin.

The Michigan lawmaker, who reportedly indicated later that he would not rule out deploying more US combat forces, joined a growing chorus of leading Democrats training fire on the White House over the best war-fighting strategy.

And Democratic Senator Dick Durbin, the party's number-two in the Senate, warned Sunday that he opposed sending more US combat forces to Afghanistan beyond the 21,000 Obama ordered there earlier this year.

"I think at this point sending additional troops would not be the right thing to do," the Illinois lawmaker told NBC television.

His comments came after Obama's top ally in the House of Representatives, Democratic House Speaker Nancy Pelosi, bluntly warned Thursday that there was little appetite among the US public or US lawmakers for sending more troops.

"I don't think there's a great deal of support for sending more troops to Afghanistan in the country or in the Congress," Pelosi told reporters.

Recent surveys have found that a majority of the US public considers the war not worth fighting, even as US-led and NATO forces in Afghanistan have suffered their deadliest year since toppling the Taliban in late 2001.

Supporters of Obama's approach worriedly predict that alleged vote-rigging in Afghanistan's presidential poll will deepen the public's resistance, which appears toughest among the White House's core supporters on the left.

Democratic Senator Russ Feingold, the first US senator to call for a timetable for withdrawal from Iraq, became in late August the first to call for a flexible timetable for withdrawal from Afghanistan.

Amid calls for an exit strategy or a clear path to victory, the administration and lawmakers plan on September 24 to unveil a list of about 50 benchmarks for measuring success in the strife-torn country.

Obama's Republican critics seem more prepared to embrace a troop increase, though they have warned that the White House needs to make a far more forceful case to the American people for why the war is necessary and how it can be won.

The White House, already struggling with titanic endeavors on health care, climate change, and the US economy, has said there will be no decision on sending more troops for "many, many weeks."

"I will reiterate again that there hasn't been a plan for and there isn't an imminent decision," White House spokesman Robert Gibbs said last week.

However, the Pentagon said Friday that a deployment of forces to counter the growing threat posed by improvised explosive devices (IEDs) was likely.

General Stanley McChrystal, the commander of US and NATO forces in Afghanistan, recently delivered a classified assessment of war strategy and is widely expected to request more US forces in the coming weeks.