President Carter signaled a turnaround in relations with Virginia Democratic leaders today by agreeing to speak at the state party's annual fund-raising dinner April 7.

State Party Chairman Richard J. Davis of Portsmouth said he is "hopeful" that the President's appearance will mark the beginning of closer cooperation between the White House and Virginia party leaders on patronage and political strategy.

Virginia party leaders were among the last in the South to support Carter in his drive for the Democratic presidential nomination in 1976 and Virginia was the only Southern state he failed to carry in the election. Since then there has been open hostility between former state party chairman Joseph T. Fitzpatrick and the White House over federal patronage in Virgina.

Davis, chosen two months ago to succeed Fitzpatrick, said he believes Carter's decision to speak at the Jefferson-Jackson Day Dinner here shows the president "has an interest in Virginia and believes it is a fertile field" for Democrats.

In response to questions, Davis said "the appraisal of the president in Virginia, is mixed," and that some conservative, business-minded Democrats have reservations about Carter. "This is incredible to me as a businessman," Davis said. "He is the best friend of business in the White House in 25 years."

Carter's acceptance is a coup for Davis and other Democrats trying to revitalize a party stricken by a bitter liberal-conservative schism. However, the appearance may focus attention on the relationship between Carter and former Lt. Gov. Henry E. Howell, whose free-wheeling populist style has been blamed by many for recent Democratic statewide defeats.

"I wonder where Henry will sit," said one Democratic official here after today's announcement. "He's got to be at the head table."

Dinner chairman Jack Horn of Charlottesville said the party hopes to net about $45,000 from the event. A $500 per couple reception is being planned prior to the dinner and dinner tickets will cost $50 each.

Davis said Democratic officials believe that Carter's speech will be the first ever by an incumbent Democratic president for a party fund raiser. Carter made three appearances in Virginia during the general election campaign in 1976 and returned in 1977 for a Williamsburg fund raiser for Howell during his unsuccessful campaign for governor.