* Tens of thousands turn out for rally along seafront road
* Opposition politicians not running in election
* Protesters oppose changes to voting rules imposed by emir
* Government urges Kuwaitis to vote, not protest
By Sylvia Westall and Mahmoud Harby
KUWAIT, Nov 30 (Reuters) - Tens of thousands of people marched in Kuwait on Friday calling for a voter boycott, a day before a parliamentary election that looks unlikely to defuse tensions in the U.S.-allied, oil-producing Gulf country.
Organisers said the march was the largest ever in Kuwaiti history and a message to the authorities of deep discontent with changes to the voting system ordered by the ruling emir, Sheikh Sabah al-Ahmad al-Sabah, six weeks before the election.
Opposition politicians are not standing in the election in protest at the emir's decree, which changed voting rules in a way they say will skew the outcome in favour of pro-government candidates. Protesters said they would shun the ballot box.
Kuwait's disaffected say they seek democratic reform, not revolution in the mould of Arab Spring revolts elsewhere. Sheikh Sabah said the amendments to voting rules were made to preserve national security and stability.
"The people want to bring down the decree!" demonstrators chanted, in a variation on the slogans of uprisings that have ousted autocratic rulers of four other Arab states.
"The message that the Kuwaiti people send ... is that they refuse the changing of the election law by the authorities," said Ahmed al-Saadoun, a former parliament speaker and now prominent opposition figure. "The number of people is a reflection that this decree must be scrapped."
Former MP Jamaan al-Herbesh, an Islamist, said the march was the largest of its kind in Kuwait's history. "The Kuwaiti people refuse elections and refuse the pro-government parliament."
Marchers in the "Nation's Dignity" rally converged on the main, palm tree-lined Gulf Coastal Road of Kuwait City and proceeded toward the landmark Kuwait Towers.
Many men, women and children wore orange clothing, the trademark colour of the boycott movement. In a carnival atmosphere, they sang songs, carried balloons and carried national flags and banners.
Police helicopters circled overhead and there was a light police presence on the ground, but no sign of the armoured trucks and riot forces deployed against previous marches.
"This (voting rule) change is against our rights," 28-year-old social worker Abdul Mohsen said. "There is corruption in the government. We want to fight corruption."
Bader al-Bader, an unemployed 33-year-old, said: "The government does not believe in having the real democracy that most people believe in nowadays. They believe Kuwait is just a big bag of money and an oil rig."
Kuwait has the most open political system among the Gulf Arab states and the government authorised Friday's march, hoping to see the opposition let off steam before Saturday's vote.
"The people are not against the ruler, they are against corruption and corrupt people, and people who think about changing the constitution," former opposition MP Musallam al-Barrak said.
Parliament has legislative powers and the right to question ministers. But the emir, head of the Al-Sabah family that has ruled Kuwait for 250 years, appoints the prime minister, who chooses the cabinet.
The emir used emergency powers in October to cut the number of votes per citizen to one from four, saying the change would fix a flawed system and maintain security and stability.
Under the old system, candidates could call on supporters to cast additional ballots for their allies. Supporters of that system say such informal affiliations are crucial in a country where political parties are banned.
The government says opposition lawmakers have used parliament to settle scores rather than helping pass laws needed for economic development. Opposition politicians accuse the government of mismanagement and have called for an elected cabinet.
The Gulf Arab state has held four parliamentary elections since 2006, after a series of assemblies collapsed because of the power struggle between elected lawmakers and the government, which has held up investment and economic reforms.
Opposition lawmakers won around two-thirds of the 50-seat National Assembly in February and formed a bloc that put pressure on the government, forcing two ministers from office.
"I am conscious that there are those who have called for a boycott of the election," Information Minister Sheikh Mohammad al-Mubarak al-Sabah said late on Thursday.
"I find this of great regret and I hope to the bottom of my heart that the 400,000-plus Kuwaitis who have the ability to cast their vote for their preferred candidate will exercise their democratic right to do so."
With opposition lawmakers opting out, the incoming parliament will include many political newcomers. A low turnout would undermine parliament's legitimacy in the eyes of many.
"The emir changed the voting rules. We believe the change has to come with the parliament. It is the parliament that represents the people," said protester Hanouf, 40, a marketing specialist who declined to give her second name.
She said current election candidates were mostly new and unqualified with "no clue how to be in parliament or politics".
The opposition, a disparate collection of moderate Islamists, Salafis and populist politicians, dominated parliament until it was dissolved after a June court ruling.
The opposition has won the backing of youth groups who have already helped organise protests against the voting rule change.
Kuwaitis often hold protest rallies outside parliament. But recent marches in the streets beyond, which authorities said were unlicensed, have been broken up by police using tear gas, smoke bombs and baton charges.