Rep. Mike Castle (R-Del.) would begin a hypothetical 2010 Senate matchup favored over state Attorney General Beau Biden (D), according to a survey released Tuesday by a Democratic polling firm based in Raleigh, N.C.

Castle, a well known moderate and the state’s former governor, led Biden, the son of Vice President Joseph Biden, 44 percent to 36 percent. The automated survey of 782 Delaware voters was conducted by Public Policy Polling March 5-8 and had a 3.5 percent margin of error.

Both men held high job approval ratings according to the PPP poll, with 54 percent of voters approving of Castle’s work in Congress and just 33 percent disapproving. Biden held a 49 percent approval rating with just 27 percent disapproving of his work as attorney general.

The elder Biden held the Senate seat from 1973 until he was elected vice president. Ted Kaufman (D), a longtime Biden aide, was appointed to replace him. But Kaufman has made it clear that he won’t run for the remainder of Biden’s Senate term in the 2010 special election.

Beau Biden is viewed as the most likely Senate nominee on the Democratic side, though he could face a primary challenge from former Lt. Gov. John Carney, who is also considering the possibility of running for Castle’s House seat.

A Castle Senate bid is viewed as less likely — not just due to the power of the Biden dynasty but also because the nine-term Congressman will be 71 in 2010. Meanwhile, public relations consultant Christine O’Donnell, the Republican nominee against Joseph Biden in 2008, is thinking of running for the Senate again.