* Kuwait votes in parliamentary election on Dec. 1
* Islamist, liberal, tribal opposition boycotting vote
* Effective boycott may hurt parliament, raise tension
* Power struggle stalls reform in US-allied oil producer
By Sylvia Westall
KUWAIT, Nov 21 (Reuters) - Kuwaitis should use the ballot box to express their demands in a parliamentary election on Dec. 1 and not take to the streets "screaming and wailing" in protest, the Gulf Arab country's ruling emir said on Wednesday.
Thousands of people have staged regular demonstrations since late October against Sheikh Sabah al-Ahmad al-Sabah's emergency decree reducing the number of votes allowed per citizen from four to one for the sake of Kuwait's "security and stability".
The opposition movement, which includes former members of parliament and youth groups, has called a boycott of the election in the major oil producer and strategically located U.S. ally situated across the Gulf from Iran.
Protests are planned on the eve of the vote in Kuwait, which has the most open political system in the Gulf, with parliament able to pass legislation and question ministers. But the emir has the final say in state matters and can veto laws.
"This tension and stress and anxiety, which hangs over our country and our society, hurts you as it hurts me," Sheikh Sabah said in comments published by state news agency KUNA.
"It is a great tragedy to have calls to take to the street," the emir said. "Why the chaos and riots? Why the screaming and wailing and disrupting the business of the state and harming the interests of the people?" the emir said.
"We have a duty to protect our country from the dangers surrounding us, the earthquakes that are shaking the Arab world."
Rallies outside parliament have been held regularly and peacefully for years, but three big marches since mid-October were broken up by police using tear gas. Protesters say they seek reform, not an Arab Spring-style revolution like those that have ousted four Arab autocratic rulers since early last year.
Analysts say the next assembly may be more government-friendly and help ease the passing of laws. But it could lack legitimacy if the election turnout is low, and may not be seen as independent - an outcome likely to raise political tensions.
The opposition - whose demands generally entail an elected cabinet including prime minister with at least some posts held by people other than relatives of the emir - held some 35 seats in the 50-seat parliament elected in February 2012.
The power struggle between the government and parliament has held up investment and economic reforms in Kuwait, one of the world's richest countries per capita. Next month's parliamentary ballot would be the fifth since 2006.
The 83-year-old emir, who is referred to as "immune and inviolable" in the constitution, said he changed voting rules to fix problems with the system, citing his "civic duty and constitutional right," according to KUNA.
"I see this as serving the interests of the country and to enhance its security and stability within the framework of the constitution and law."
In Kuwait, home to 1.2 million Kuwaitis and 2.5 million foreigners, the emir can dissolve parliament - last done on Oct. 7, and can issue urgent decrees when parliament is not in session.
Elections in February 2012 ushered in a parliament with an opposition majority, made up of Islamist, tribal and liberal MPs, which raised pressure on the government. That opposition bloc is boycotting the elections.
Sheikh Sabah said national unity was needed to tackle internal challenges and to protect against external threats.
"We have anti-corruption challenges, and (need) comprehensive reform of all state organs, the education system, public services, health, electricity and water," he said.
Work was also needed on transport, housing and providing thousands of jobs for young people.