At every stop, blacks riveted him with horror stories of voting discrimination, and by the time the assistant attorney general in charge of civil rights stepped to the pulpit of the little black church here today, he had a gleam in his eye and a lilt to his speech. Some even suggested he was getting a touch of soul.

Indeed, the education of William Bradford Reynolds, wealthy Delaware aristocrat, top Reagan aide and frequent target of criticism over civil rights enforcement, was a sight to behold. He was fired up.

He had caught the spirit of Jesse Jackson, his tour guide to the rural outback of the Mississippi Delta.

"I've heard the difficulties you have in access to registrars," he preached, eliciting amens.

"I've heard about the polling places that were moved . . . and intimidation at the ballot box. I urge you to step forward so I can hear your story."

And they did step forward, striding to the pulpit of Pleasant Green Holiness Church to testify to their grievances.

Reynolds vowed later to do something about them.

"We're going to look at these complaints pretty damn carefully to see how many problems are real ones, and I think there are some real ones, and correct them," he said in an interview.

But he will have to hurry. There is little time left to register for the statewide primary on Aug. 2.

Reynolds, one of few top Justice Department officials to scout voting irregularities in Mississippi since Robert F. Kennedy, said the trip had opened his eyes.

He scribbled notes as a black Greenwood attorney told of a white man who intimidated black voters by impersonating a Justice Department official.

"I never heard of anything like that before," he reflected over grits and eggs at Foster's Diner in Belzoni.

"It's one thing to read a complaint on paper and quite another for someone who has been wronged to get up and say it with feeling. It's something you can't get in Washington, D.C."

Reynolds booked the flight to Mississippi after Jackson went to Washington last Friday to tell about wide-scale voting discrimination against blacks he has found traveling the South in a massive voting registration drive.

At Jackson's urging, Reynolds brought along his top lieutenants in the Civil Rights Division, and Tuesday they piled into a 26-foot Winnebago--dubbed the "Justice Buggy" by Jackson--to begin a two-day Mississippi odyssey that took them through the heart of the Delta, from Greenville to Belzoni and beyond.

At the wheel was a black Memphis businessman, his "fuzzbuster" radar speed trap detector bleeping caution as he whisked the strange bedfellows down winding two-lane blacktops to hear the people's complaints.

Jackson, flirting heavily with the notion of a black presidential candidacy, lectured Reynolds nonstop, regaling him with civil rights war stories.

Though Reynolds has been criticized repeatedly by black leaders for his opposition to affirmative action quotas and mandatory school busing, he was warmly received today, linking arms with Jackson and singing "We Shall Overcome" at every stop.

As the caravan rolled into Belzoni, Victor McTeer, a black lawyer who handles many voting rights cases, told Reynolds how the town of 3,200 had kept white control by refusing to annex a black neighborhood in the heart of town.

"Sounds like the town should be embarrassed," Reynolds said.

Later, he heard other accounts of rural towns annexing white neighborhoods to dilute black voting strength. Canton was among those Jackson charged with relocating blacks outside the city limits in federally built housing.

Others told of being forced to register twice by law (once in the city, then in the county), of recalcitrant officials unwilling to set up satellite registration and of plantation-style intimidation.

Johnny Thomas, mayor of Glendora, accused whites in Tallahatchee County of paying blacks $10 each to return blank ballots. Mamie Chinn, a black poll worker from Canton, said that in 1980 she watched an elderly black man mark his ballot for black candidates until his white boss wandered over to chat. The old man then tore up his first ballot, asked for another and voted for the whites, she said.

Reynolds promised to establish liaison with Mississippi civil rights lawyers, a hot line to Washington, in effect, to provide a quick response to Voting Rights Act complaints. Aides noted that Justice has objected to 10 of 82 Mississippi counties' redistricting plans.

Jackson, meanwhile, promised to overload the system with lawsuits challenging Mississippi's dual registration and voting procedures as violations of the Constitution and the Voting Rights Act.

"You've got an election coming up and we're going to see it conducted in the fair manner Congress said you all are entitled to have under the Voting Rights Act," Reynolds said.

But few blacks here saw the foray by Reagan's top civil rights official--hard on the heels of two stinging reports by the Civil Rights Commission--as a true conversion by an administration suffering from an anti-black image.

"Even if Reynolds did something about our problems, I'd see it as a last-minute effort to send Reagan back to the White House," said Larry Neal, 33, a Greenwood arcade owner. "I don't think blacks should be deceived by the tactic."