PANAMA CITY: Panamanians go to the polls Sunday to decide who will lead this small but strategically vital isthmus nation, which sits at a major crossroads for world trade.

Voters will choose a new president between supermarket mogul Ricardo Martinelli, who has vowed to run the country like a company, and Balbina Herrera, a one-time leftist firebrand with links to former dictator Manuel Noriega.

Balloting is scheduled to begin at 7:00 am (1200 GMT) and end at 4:00 pm (2100 GMT).

Martinelli -- a 57-year-old multimillionaire whose business empire includes supermarkets, banks and agriculture firms -- has the lead going into the vote, despite government backing for his rival, who is known across the country as "Balbina."

Despite breakneck economic growth -- led by a construction boom that has transformed Panama City's skyline, which now looks more like Manhattan than other Central American capitals -- both campaigns have focused on bringing wealth to the poorest Panamanians.

Massive income disparities still exist in the tropical nation, where 28 percent of the population of more than three million lives in poverty.

In the capital, slums made of wooden houses exist a stone's throw from the presidential palace, in a Spanish colonial quarter that is home to jazz clubs, boutique hotels and upscale ice-cream parlors.

Martinelli has tapped in to popular discontent, promising to "walk in the shoes" of the ordinary citizens, who have been hit by rising prices.

Much of the country's wealth remains in the hands of a few families with European roots.

Polls show him ahead of Herrera by between 11 and 16 points.

Whoever wins the vote will oversee a 5.25-billion-dollar project to expand the congested Panama Canal, by adding a third set of locks that can handle ships laden with up to 12,000 containers each.

The 55 mile (80 kilometer) inter-oceanic waterway handles an estimated five percent of world trade, and most of the trade in goods between China and the east coast of the United States.

After an early lead, Herrera has suffered from a wave of criticism of the ruling center-left Revolutionary Democratic Party (PRD), which many accuse of not doing enough to redistribute vast income from shipping, banking, construction and multi-billion dollar bond sales.

The PRD has also been criticized for failing to tackle fragile public safety, particularly in Panama City and the down-at-heel Atlantic port city of Colon.

Current president Martin Torrijos -- the son of former general Omar Torrijos who was mysteriously killed in a plane crash -- has come under fire for failing to reform Panama City's sclerotic public transport system.

Today the capital is served by a network of privately-owned clapped-out US school buses, know to locals as Diablos Rojos, or "red devils."

Under Panama's constitution Torrijos is ineligible to two consecutive terms, which led to the PRD selecting Herrera as its candidate.

But Herrera, a former minister of housing, has also been criticized for her ties to questionable figures, notably David Guzman, the architect of a multi-million Colombian pyramid scheme who has said he gave her three million dollars.

In his memoirs Manuel Noriega also claimed he hid at Herrera's house from US soldiers who invaded Panama and overthrew him in 1989.

Herrera denies links with the two men.

Still analysts say there is little chance of either candidate overhauling Panama's staunchly pro-market outlook.

"None of the two candidates will put the system in danger" Aristides Hernandez, the president of Latin Consulting told AFP.

But Hernandez warned that "exaggerated campaign promises" have created expectations that will be difficult to fulfill.

Some 2.2 million people are eligible to vote. Voters will also elect 71 members of the national assembly, mayors and members of municipal councils.