U.S. Rep. Mazie Hirono and former congressman Ed Case are in a close race in the Democratic primary for the U.S. Senate, according to a new Public Policy Polling survey.

The poll showed Hirono at 45 percent and Case at 40 percent. The margin of error was 5.1 percentage points.

Hirono led former Gov. Linda Lingle, a Republican, 48 percent to 42 percent in a hypothetical general election matchup. Lingle had the edge over Case, 45 percent to 43 percent. The margin of error for the general election matchups was 4.1 percentage points.

The automated telephone poll was taken among 568 voters — including 368 usual Democratic voters — from Oct. 13 to Sunday. Public Policy Polling is a Raleigh, N.C.-based polling firm.

A Public Policy Polling survey taken in March showed Case ahead of Lingle by 17 percentage points and Hirono ahead of Lingle by 12 points.

"This race has become far more competitive since PPP last polled it in March," Dean Debnam, president of Public Policy Polling, said in a statement. "Linda Lingle’s candidacy does give Republicans a chance for a pickup that would be devastating to Democratic hopes of holding onto the Senate."

Case has said that one of the most important questions for Democratic primary voters is which candidate can beat Lingle in the general election. He has suggested that Hirono — who lost to Lingle in the 2002 governor’s race after beating Case in the primary — would be unable to defeat the former governor.

Public Policy Polling also found that Hawaii Republicans prefer business executive Herman Cain to former Massachusetts Gov. Mitt Romney in the Republican presidential campaign.

Cain had 36 percent, while Romney had 24 percent. The automated telephone survey was taken among 293 Hawaii Republicans from Oct. 13 to Sunday. The margin of error was 5.7 percentage points.

The Hawaii Republican caucuses are on March 13.