KABUL, Afghanistan  For all the fighting that lies ahead over the next several days, no one doubts that the American and Afghan troops swarming into the Taliban redoubt of Marja will ultimately clear it of insurgents.

And that is when the real test will begin.

For much of the past eight years, American and NATO forces have mounted other large military operations to clear towns and cities of Taliban insurgents. And then, almost invariably, they have cleared out, never leaving behind enough soldiers or police officers to hold the place on their own.

And so, almost always, the Taliban returned  and, after a time, so did the American and NATO troops, to clear the place all over again.

“Mowing the grass,” the soldiers and Marines derisively call it.

This time, in Marja, the largest Taliban stronghold, American and Afghan commanders say they will do something they have never done before: bring in an Afghan government and police force behind them. American and British troops will stay on to support them. “We’ve got a government in a box, ready to roll in,” said Gen. Stanley A. McChrystal, the top American commander here.