CHICAGO - FROM protecting pregnant pigs to banning gay marriage and abortion or boosting the use of renewable energy: US voters will have more decisions on Tuesday to make than just picking their president.

Some 153 such questions have been placed on statewide ballots this year and voters will face scores more from their municipal or county governments.

Many of the ballot measures are mandated by state law, but others are 'citizen initiatives' pushed by a variety of special interest groups.

'The initiative movement came up as a way to provide an outlet when the legislature is not responding to popular demand,' said Ms Jennie Drage Bowser, a policy analyst at the National Conference of State Legislatures.

'What's on the ballot reflects what Americans are thinking about and talking about', she explained.

'In the 1930s it was labour issues. If you look at what's been on the ballot in the last five years it's same sex marriage and the minimum wage'.

The Humane Society is responsible for getting Californians to consider a new law protecting pregnant pigs, egg-laying hens and calves raised for veal from being kept in cages so cramped they cannot move around, stand or lie down.

A coalition of conservative groups is trying to reverse a recent California Supreme Court ruling that it is unconstitutional to ban gay marriage with an initiative to amend the state constitution to define marriage as only between a man and a woman.

California also has initiatives which would decriminalise the possession of small quantities of marijuana and expand drug treatment for criminals, increase the use of renewable energy, and require a waiting period and parental notification for teenagers seeking an abortion.

Abortion opponents have also placed an initiative on the ballot in South Dakota to ban abortion except in cases of rape, incest or a threat to the mother's life.

And there is a move to amend Colorado's constitution to define the term 'person' so that legal rights begin 'from the moment of fertilisation'.

That initiative would then define abortion - or even the use of the morning after pill - as murder and could result in complex legal fights over the property rights of fetuses.

These measures would face immediate challenge if passed, but abortion opponents hope they may find a more hospitable Supreme Court should the justices be willing to reopen the question.

While many ballot initiatives have successfully driven national policy, there is another more immediate purpose, Mr Bowser said.

'A controversial ballot initiative can boost turnout by three or four points,' Mr Bowser said.

Controversial initiatives are often placed on the ballots of battleground states, such as a ban on gay marriage in Ohio, which handed Mr George W. Bush his second term as president with a narrow margin of less than 120,000 votes in 2004.

A similar ban is proposed in the swing state of Florida this year while voters in battleground Missouri will be asked if the constitution should be amended to make English the official language amid tensions over immigration.

Republican presidential hopeful John McCain's home state of Arizona has eight initiatives on the ballot, including: - a proposal to amend the state constitution to define marriage as being 'only a union of one man and one woman' and thus block gay marriage - a crackdown on those who employ undocumented workers, which includes permanently revoking business licenses for companies that knowingly hire them - and a plan to raise the salaries of state legislators from 24,000 US dollars to 30,000 US dollars a year (S$35,341 to S$44,172).

Democratic rival Barack Obama's state of Illinois has just a single initiative on the ballot: a mandated request to ask voters if they want a convention to review the state's constitution.

Other initiatives across the country are aimed at reversing affirmative action policies, reforming campaign finance rules, limiting taxes, making it harder for unions to collect dues or get members, and prohibiting unmarried couples - be they gay or straight - from adopting or fostering children. -- AFP