Tunisian Prime Minister Beiji Caid Essebsi speaks during an event at the World Bank in Washington, D.C. (JEWEL SAMAD/AFP/GETTY IMAGES)

Islamists are poised to do well in elections this month in Tunisia, the first of the Arab Spring countries to choose new representatives. But the nation’s prime minister has a message for the West: Don’t worry.

“All Islamist parties are not the same,” Beji Caid Essebsi said in an interview Wednesday.

Opinion polls indicate that an Islamist party, Ennahdha, could get the most votes in the Oct. 23 balloting, in which voters will choose an assembly to rewrite Tunisia’s constitution.

“There’s a red line on which we all agree,” Caid Essebsi said, which is to maintain the 1959 constitution’s definition of Tunisia as a Muslim country — but “not an Islamic republic.”

The head of Ennahdha, Rachid Ghannouchi, recently told Reuters that his party “will not retreat” from modernizing reforms instituted after Tunisia became independent. He says the party respects democracy and women’s rights. Some secular groups, however, are worried.

Caid Essebsi, 84, was a longtime senior official in Tunisia’s authoritarian governments, which were strongly opposed to Islamist movements, although he was seen as something of a reformer. During his visit to Washington this week, Caid Essebsi plans to thank President Obama for his support of the January revolution that ousted President Zine el-Abidine Ben Ali.

But Caid Essebsi also is hoping for more support, particularly to help the ailing economy.

“The revolution in Tunisia has to succeed in order to serve as an example for others in the region,” he said.

The Obama administration has proposed economic “enterprise” funds to help small businesses in Tunisia and Egypt. But it is still unclear whether Congress will sign off on the idea.

In addition, a major U.S. aid agency, the Millennium Challenge Corp. (MCC), announced last week that Tunisia will be eligible for one of its “threshold” grants, which are usually between $10 million and $20 million. But the country did not qualify for the agency’s higher-level “compact” grants of $200 million or more.

“It wasn’t nice news,” Caid Essebsi said.

Sheila Herrling, vice president for policy evaluation at the MCC, said Tunisia hadn’t met the requirements for democratic governance.

“But we are really, really excited about the opportunity that the threshold program will bring for engagement in Tunisia,” she said.