Southern Republicans attending a 13-state leadership conference here today say that George Bush's victory in Iowa has made him a threat to the candidates believed strongest in this conservative region -- Ronald Reagan and John Connally.

Republican leaders said that Bush's first-place finish has given him the winning image that they are looking for in 1980.

Although Bush now lives in Houston, he is a native New England Republican and has not always been a favorite among Deep South Republicans. r

Harry Dent of South Carolina, one of the most important Republican strategists in the South, said he volunteered to support Bush after the former ambassador and ex-CIA director defeated Reagan and Connally in Iowa.

"Bush can win the support of conservatives," Dent said, "but he has a streak of lean -- a streak of lean in you in order to go all the way [against the Democratic nominee in November]."

Dent will be Bush's campaign manager in South Carolina, where Republicans hold their first southern primary March 8.

Dent says he thinks Connally, a former Democratic governor of Texas, would make a good a president, but the Iowa results confirm suspicions that Connally cannot win in 1980.