At 1:30 p.m. the temperature rose above 100 in the Mississippi Delta, and the Rev. Henry Ward, whose campaign slogan was "Let God's Representative Represent You," said he was worried.

"The turnout isn't what we'd expected," he said outside the Mound Bayou City Hall, polling place for the largest black precinct in Bolivar County. "We're just hitting 600 now. We should be over 800."

Twenty years ago, when civil rights workers came into the Delta, Mound Bayou, an all-black town founded in 1887 by former slaves, was where they gathered for safety and relaxation when the sun went down.

Ward, born on a plantation near here, hoped the town would give him enough votes today to make him the first black from this county in the modern-day Mississippi House of Representatives.

His hopes were dashed tonight when he was defeated by incumbent Rep. Edward G. Jackson.

Although Ward's district is 77 percent black--Mississippi has the largest proportion of blacks nationwide at 35 percent--he said he faced an uphill battle because of low black turnout. Blacks tend not to participate in runoff elections like this one in Mississippi.

"They've always felt the vote was going to go the way the whites wanted it anyway, and there wasn't any use in it," said Moses Williams, a black poll watcher in neighboring Washington County.

But Ward and other black political leaders maintain that, 18 years after passage of the federal Voting Rights Act, Mississippi's electoral system discriminates against black candidates.

They persuaded the Justice Department to send 380 federal election observers from Washington, D.C., to monitor today's elections. The Rev. Jesse L. Jackson, director of Operation PUSH (People United to Save Humanity) and a potential black candidate for the presidency, wanted 300 more. There were 64 in Bolivar County, more than in any other county.

While visiting polling places today, Jackson said he had asked William Bradford Reynolds, head of the Justice Department's Civil Rights Division, to investigate a murder and a church burning that he said may have been civil rights violations.

He said Pertis Williams, who had hosted a Jackson visit to the town of Brookhaven, was murdered last week. Police said there is no evidence to connect the murder with Jackson's civil rights activities.

He also said a poster advertising one of his rallies was pasted on a Humphreys County church that was burned early Sunday. A white man has been charged with arson in that incident.

"I don't think these things are coincidental," Jackson said. "All of them are part of a process of discrimination and intimidation."

Black candidates in Washington County said another incident that coincided with Jackson's Greenville visit gave their candidacies a much-needed boost. Fifty voting machines in Washington County malfunctioned during the primary election on Aug. 2 while Jackson was there.

Officials blamed the malfunctions on mechanical problems, but black leaders charged that the troubles were part of an effort to damage black candidates.

"In plain old-fashioned language, this has gotten people as mad as hell," said state Rep. Leslie King of Greenville. "You can call it human error. But it's just highly unlikely that 50 machines wouldn't work."

Black leaders long have complained that white election officials have held down black voting strength through gerrymandering, annexation, runoff primaries and dual registration, in which voters must register both in their local communities and at the county seat.

Jackson, who first came to the Delta as a young civil rights activist 20 years ago, has put these concerns into everyday language that has become a popular rallying cry here.

Jackson is telling enthusiastic audiences that white politicians here have outmaneuvered federal voting laws.

"They have new names for old games," he said. Some cities, Jackson charged, have built public housing units with government funds outside their city limits so that blacks who live in them won't be able to vote in local elections. Other cities, he said, have annexed white suburban areas to dilute black voting strength.

"Annexation means when we come to bat, they move the fence back," he said.

This kind of remark touches a receptive chord among black leaders like Earl Lucas, mayor of Mound Bayou for the last 16 years.

He said that blacks, who live just outside his city limits, are forced to travel 3 1/2 miles to vote in the neighboring town of Merigold.

In Clarksdale, the county seat, residents of the southern, heavily black part of the city have to travel to the nearby town of Boyle to vote. In other rural areas voters have to travel as far as 20 miles to cast their ballots.

Jackson has made two trips to this part of Mississippi during the last month as part of a get-out-the vote drive. He has created both controversy and enthusiasm.

Leslie King is one of 17 blacks in the legislature, a number that civil rights leaders don't expect to grow by more than two or three this year.

Monday night Jackson, appearing before a crowd of more than 300 people, said today's election, "is test time for democracy. It's test time for the Democrats. It's test time for the Justice Department."

Jackson was joined on the stage by two black candidates, Laverne Moore and Estelle Pryor.

Moore was running for tax collector, Pryor for clerk of circuit court. Both have worked as deputies in the two county offices for more than a dozen years.

"We're not seeking these offices for our own selves. We're seeking to serve you," Pryor told the audience. "My background is as chief deputy clerk. I'm there. I claim it. I can't put it down."