ST. CHARLES, Mo. (AP) _ Flood officials had feared the worst for weeks. Friday, it happened: The Missouri and Mississippi rivers joined their muddy forces about 20 miles inland from their usual confluence.

A levee broke in at least four places on a thin peninsula between the two rivers in soggy St. Charles County, north of St. Louis, allowing Missouri River floodwaters to pour into Mississippi River backwash.

Military trucks were used to rescue some people who had ignored evacuation orders. Some 7,000 people living in the villages and farms of the flood plain had been urged for a week to leave their homes because of the building threat.

In some places, the Mississippi had already encroached into the county as far as nine miles. In narrow places, the Mississippi lapped against the levee, which strained to hold back the Missouri. On Friday, the waters met.

Freed of its bounds, the Missouri began streaming northward across the county to join the Mississippi, somewhere near Portage Des Sioux, said Gary Dyhouse of the Army Corps of Engineers.

Because of the way the land slopes, the Missouri is now following a meandering channel abandoned centuries ago, Dyhouse said. The river will follow this temporary course until it drops below flood stage.

The National Guard set up a ferry service between Portage Des Sioux and dry land Friday. Marooned residents boarded giant military transport rafts to travel back and forth to their homes across the scummy Mississippi.

To make sure people could reach the rafts, highway workers built a temporary levee of recycled asphalt along Highway 94, hoping to hold back the Mississippi at a key intersection.

An estimated 85 square miles, about a third of the county, was already flooded before the levee breached, said Petra Haws of the St. Charles County emergency management agency. Most of St. Charles itself, population 55,000, is on higher ground and will likely avoid flooding.

It took sheriff's deputies and National Guardsmen to persuade Sherry Sue Nestor, 33, and her father, Ralph Nestor, 68, to leave their trailer through shin-deep water. Currents from levee breaks could knock the trailer off its foundation, the two were told.

Ms. Nestor was reluctant. ''Our belongings are there and we're afraid people will loot and take what little we've got left.''

But she finally came out, carrying their black cat, Whoopie, and a plastic grocery bag full of her belongings.

Even with water flowing across the roads and abandoned toys bobbing in the current, not everyone was ready to go.

One man relaxed in a lawn chair set in the shade on one of the drier streets, not far from his trailer. Black rubber boots sat on the road next to him, and he had a coffee cup and a pack of Pall Malls near at hand.

Cool in shorts, aviator shades and several gold chains, he said he was standing guard.

''This is my way of helping,'' he said, declining to give his name. ''I'm not in it for glory.''