River towns downstream from Jackson, Miss., felt the early shocks of an "inevitable" heavy flood yesterday, while in several other states, thousands of families were uprooted by rising waters.

The Tombigee River at Demopolis, Ala., crested yesterday morning at 25 feet above flood stage, highest water mark since the area was settled in 1818 by French regugees from the Battle of Waterloo.

The swollen Red River went on its annual tear through the flat farmland of North Dakota and western Minnesota, prompting Minnesota Gov. Al Quie to dispatch National Guard troops to the towns of Crookston and East Grand Forks.

In Texas, the San Jacinto River erested at four feet above flood level at Conroe, near Houston, where 800 to 1,000 persons are homeless.

Three miles south of Austin, Tex., 40 horrified onlookers watched as the raging current of Slaughter Creek ripped 48-year-old Virginia Craig from her husband's arms as both clung to a tree after their car was washed into the torrent.

The mayor of Minot, N.D., said that he may order the evacuation of 12,000 persons in lowlands along the Souris River. He said the water level was suddenly approaching that of a 1976 flood that forced a general evacuation.

In Mississippi, the Pearl River which earlier this week routed 17,000 persons in Jackson and left damage estimated at $500 million, was bearing down on smaller communities to the south.