The worst Pearl River flood in history surged deeper into the heart of Jackson today, sending water to the eaves of some homes in the suburbs and forcing officials to seal off the down-town area.

With an estimated 17,000 persons already driven from their homes, the river poured over sandbag levees and inundated more houses, businesses and public facilities, including the city's new $48 million sewage treatment plant. Mayor Dale Danks ordered police to seal of downtown as workers battled to keep floodwater from knocking out a key electric substation supplying power to the area.

Police turned away all but non-essential workers to prevent sightseers from interfering with emergency operations and dump trucks bringing in dirt for sandbags.

The levees were holding, but the water surged over the top in spots as the Pearl reached almost 43 feet at jackson, nearly 25 feet above flood stage and well above the previous record of 37.5 feet set in 1902. The river was expected to crest at 43 feet sometime tonight.

"We think the peak will come pretty soon," said Dave Waite, a city spokesman. "We're praying that's the case."

Flooding followed the winding course of the river of Jackson's east side. It has sent floodwaters up to the ceilings of expensive homes in northeast residential areas, overflowing into shopping centers and shops, pushing into downtown streets and spreading over low-lying areas in the southern part of the city.

Schools were closed indefinitely and were turned into emergency shelters.

Gov. Cliff Finch said late today that President Carter has declared Mississippi a federal disaster area, making flood victims eligible for temporary federal housing and low-interest loans for repairs.

Finch estimated that flooding damage statewide was already in the "millions and millions of dollars" and civil defense officials warned that destructive flooding could continue later this week.

Jackson residents were urged to cut back on water usage yesterday after the city pumping station was flooded.

Mayor Danks, weary from three nights without sleep, stressed that there was no danger to the water supply and that at no time during the crisis was unsafe water pumped into the system.But he ordered curtailed use of the water by business and industry until more temporary pumps could be set up.

Danks said the city was receiving about half its normal water supply because main pumps had flooded and emergency pumps were unable to maintain the volume.

Authorities closed north-south Interstate 55 through Jackson on Sunday when sections were flooded. Interstate 20, an east-west highway, was open, but police prevented motorists from using downtown exits, creating a Monday morning traffic jam that lasted several hours.

Eight deaths were attributed to flooding in the state, including four persons who drowned Sunday near Iuka when rough waters capsized their fishing boat on the Tennessee River. CAPTION: Picture, Most of these Jackson, Miss., homes, in a well-to-do area, are almost new. Statewide damage will be "in the millions and millions," Gov. Cliff Finch said. AP