NEW ORLEANS (AP) — Legal roadblocks will likely doom an effort launched this week to recall U.S. Rep. Ahn ‘‘Joseph’’ Cao, the Vietnamese Republican who scored a surprise December victory in a predominantly black, mostly Democratic New Orleans congressional district.

Still, the petition drive, started by two black ministers only weeks after Cao took office, demonstrates the challenges he’ll face if he seeks a second term in 2010.

‘‘At this point it’s going to be more symbolic than substantive,’’ pollster and political consultant Silas Lee said Friday of the recall effort, ostensibly launched to protest Cao’s vote against the federal stimulus package. ‘‘But symbolism carries a powerful message.’’

Legal experts say a sitting congressman cannot be removed by voters before his term ends. A report last year by the nonpartisan Congressional Research Service said it can’t be done and Louisiana Secretary of State Jay Dardenne asked Friday for an opinion from the state attorney general.

Cao’s December election was a stunner. It dislodged once-powerful 18-year incumbent William Jefferson, a Democrat who was the state’s first African-American congressman since Reconstruction.

Cao was helped by unusual circumstances in a district where voter registration is almost two-thirds black and more than two-thirds Democratic.

Jefferson was weakened by a federal indictment accusing him of taking bribes. And because Louisiana’s election cycle was delayed by two hurricanes, the general election was held Dec. 6, when there was no Barack Obama at the top of the ballot to help generate black voter enthusiasm. In a low-turnout election, Cao won with just under 50 percent over Jefferson, who had 47 percent, and two minor party candidates.

Cao, 41, rose to prominence in the 2nd Congressional District as an attorney, community activist and a leader in the recovery effort of a small but thriving Vietnamese community hit hard by Hurricane Katrina in 2005.

After the election he promised to work across racial and party lines to continue the recovery, and he broke with his party with an early vote to expand a children’s health insurance program.

But his two votes against President Barack Obama’s stimulus package prompted the recall effort, said Rev. Aubry Wallace, chairman of the petition drive, and Rev. Toris Young, president of the Louisiana Ministerial Alliance of Churches for All People.

Young predicts a huge public outcry if the requirements for a recall are met and Cao remains in office.

‘‘How can they elect on official and then they can’t recall him?’’ he said.

He noted that the Congressional Research Service report says the Supreme Court has never ruled directly on the question of a congressional recall and said if a successful recall is thwarted by a legal challenge he would fight it to the Supreme Court level.

Perhaps as daunting as the legal questions is the logistical challenge. To recall a state official in Louisiana requires the gathering of verifiable signatures from a third of the district’s active voters in six months — more than 101,000 signatures.

Young expressed confidence, however. He said his alliance has 165 churches, 20,000 members and 480 ministers. The recall effort has 300 volunteers and had already gathered 13,000 signatures by midweek.

Even if Cao isn’t recalled, such an organization could provide a formidable base for anyone who wants to oppose him in 2010.

The effort sends a powerful signal, Lee said.

‘‘He’s only been in office a little more than a month and this does send a strong symbolic message, depending on how many signatures they get, that the voters in the 2nd district will closely watch his voting record and how effective he is,’’ Lee said.

Cao and his aides defend the anti-stimulus vote, saying the package added too much to the national debt and a White House analysis indicate the plan would create few jobs in Cao’s district.

‘‘Our goal is to work with every body in the district,’’ said Cao aide Murray Nelson. ‘‘We invite the ministers to join us.’’