Last chance for Ivory Coast's Gbagbo to avoid force-rival

* ECOWAS envoys to resume talks with Gbagbo this week

* Security heightened at Ouattara&${esc.hash}39;s hotel headquarters

* Gbagbo aide says presidency "non-negotiable"

(Adds Gbagbo camp reaction, paragraphs 2, 8)

By Tim Cocks

ABIDJAN, Jan 1 (Reuters) - Ivory Coast&${esc.hash}39;s Laurent Gbagbo has only days in which to leave power peacefully with immunity, the prime minister of Ivory Coast&${esc.hash}39;s presidential rival Alassane Ouattara said on Saturday.

A senior aide to Gbagbo said that while the incumbent was open to talks, his staying on as president was "non-negotiable."

Three presidents from West African regional bloc ECOWAS are planning a second round of talks on Jan. 3 with Gbagbo in an effort to convince him to cede power to Ouattara or face force after last month&${esc.hash}39;s disputed election.

"The message seems clear. This is the last chance for Mr. Gbagbo to get a peaceful departure from power and a guarantee of immunity," Ouattara&${esc.hash}39;s Prime Minister Guillaume Soro told reporters at the Golf Hotel, his rival governments&${esc.hash}39; headquarters protected by some 600 U.N. peacekeeping troops.

Earlier, a spokesman for Ouattara said ECOWAS must use military force soon or Gbagbo would become entrenched in power and become more difficult to remove.

Gbagbo has shown no sign of giving in to growing international pressure to step down as leader of the world&${esc.hash}39;s top cocoa grower since a top court, run by one of his allies, overturned a Nov. 28 election result that gave Ouattara victory.

The United States says more than 200 people have been killed since the standoff, which has threatened to restart a 2002-03 civil war. The United Nations has said Gbagbo may be criminally responsible for human rights violations, including killings and kidnappings by security forces.

"We are ready for dialogue with ECOWAS," Gbagbo&${esc.hash}39;s campaign manager Pascal Affi N&${esc.hash}39;Guessan told Reuters by phone. "But he (Gbagbo) won&${esc.hash}39;t leave ... We won&${esc.hash}39;t negotiate on that question."

The United States and the European Union have imposed sanctions on Gbagbo and his inner circle while the World Bank and the West African central bank have cut off his financing in an effort to weaken his grip on power.

ECOWAS defence chiefs met last week in Nigeria to work on a possible intervention plan.

"Neither sanctions nor international pressure have convinced Gbagbo to leave power," Soro said. "I am calling for the use of legitimate force. We have yet to see a dictator leave power peacefully."

A Gbagbo spokesman was not immediately available. Asked on Friday if he would leave in the event of an ECOWAS operation to remove him, Gbagbo told Euronews television: "I will see, I&${esc.hash}39;ll think it over. But for the moment it&${esc.hash}39;s not an issue."

Soro said he asked the New Forces rebels still occupying the north since the civil war not to intervene, but to support whatever force does arrive to kick out Gbagbo.

Fearing a possible march by Gbagbo supporters, U.N. riot police armed with shields and teargas did drills along the road leading to the lagoon-side Golf Hotel, where U.N. troops stand guard at sandbagged machinegun positions.

The roads have been blockaded by the Ivorian military since a shootout between pro-Gbagbo and pro-Ouattara forces on Dec 16. Only U.N. helicopters can get in or out, apart from the occasional supply truck.

"We&${esc.hash}39;re trapped," said Ouattara supporter Traore Dramane, 24, an importer, who sleeps on the floor in a makeshift dorm. "It&${esc.hash}39;s too dangerous to leave. There are military forces everywhere. If I try to leave I might get killed." (Writing by Richard Valdmanis; Editing by Janet Lawrence)