* Gathering in east Libya says will run own affairs
* East is home to Libya's biggest oil fields
* People in region complain of neglect by Tripoli
* NTC leader says autonomy bid could wreck Libya (Updates with protest in Benghazi)
By Issam Fetouri
BENGHAZI, Libya, March 6 (Reuters) - Delegates announced plans for greater autonomy on Tuesday in the Libyan city of Benghazi, prompting an immediate warning from the central government of a foreign-inspired plot to break up the country.
About 3,000 delegates in the eastern city announced they were setting up a council to run Cyrenaica, the province which is home to Libya's biggest oil fields, in defiance of the government in Tripoli.
The declaration tapped into longstanding unhappiness in the east of Libya at what it regards as neglect and marginalisation by the rulers in the capital, more than 1,000 km (620 miles) to the west.
It deepened the troubles of the National Transitional Council (NTC), the body internationally recognised as Libya's leadership after last year's rebellion ousted Muammar Gaddafi. The NTC is already struggling to assert its authority over militias and towns which pay little heed to Tripoli.
"I regret to say that these (foreign) countries have financed and supported this plot that has arisen in the east," NTC chairman Mustafa Abdel Jalil told reporters.
"I call on my brothers, the Libyan people, to be aware and alert to the conspiracies that are being plotted against them and to be aware that some people are dragging the country back down into a deep pit."
Moves towards greater autonomy for Cyrenaica -- the birth-place of the anti-Gaddafi revolt -- may worry international oil companies operating in Libya because it raises the prospect of them having to re-negotiate their contracts with a new entity.
A member of staff who answered the phone at Benghazi-based Arabian Gulf Oil Company (Agoco), Libya's biggest state-owned oil firm, said the 3,000 employees had been deliberating about whether or not to back the autonomy declaration.
"Some people are in favour and some people are against but there is no official stance yet," the Agoco employee said.
Several hundred people gathered in Benghazi on Tuesday night to protest against the push for autonomy. They carried placards saying: "No to federalism."
The congress in Benghazi named Ahmed al-Senussi, a relative of Libya's former king and a political prisoner under Gaddafi, as leader of the self-declared Cyrenaica Transitional Council.
An eight-point declaration said the "Cyrenaica Provincial Council is hereby established ... to administer the affairs of the province and protect the rights of its people".
It said, though, that it accepted the NTC as "the country's symbol of unity and its legitimate representative in international arenas."
The declaration in Benghazi does not carry legal force. It was not clear if the Cyrenaica council would operate within the framework of the NTC, or as a rival to it.
One analyst said the congress in Benghazi would change little on the ground.
"Today's statement from Benghazi was more a declaration by a group in favour of a high degree of autonomy, rather than a declaration of that autonomy itself," said Alex Warren, a director of Frontier, a Middle East and North Africa consultancy.
"In reality, Libya is now effectively composed of many de facto self-governing towns and cities, overseen by a weak central authority," he said.
"The process of integrating these into a new political and economic structure will be volatile ... but I don't necessarily see it as the spark for any major civil conflict."
Cyrenaica stretches westwards from the Egyptian border to the Sirte, half-way along Libya's Mediterranean coastline.
The province enjoyed prestige and power under King Idris, Libya's post-independence ruler, because the royal family's powerbase was in the east.
But when the king was toppled by Gaddafi in a military coup in 1969, eastern Libya was sidelined for the next four decades. Residents complain that they have been denied a fair share of the country's oil wealth.
The rebellion last year which overthrew Gaddafi gave new impetus to calls for local self-determination in the east. These became even more vocal as frustration grew with the slow pace at which the new leadership in Tripoli was restoring order and public services after the revolt.
Some Libyans have dismissed the moves for autonomy in eastern Libya as a ploy by a coterie of wealthy families who had prospered under the old monarchy. (Additional reporting by Ali Shuaib, Christian Lowe and Hisham El Dani in Tripoli; Writing by Christian Lowe; Editing by Michael Roddy)