California is the biggest prize in the primary elections and caucuses Tuesday, known as Super Tuesday, when voters in more than 20 states will choose their nominees for the presidential election. California offers the largest number of delegates for the nominating conventions of both parties. Mike O'Sullivan reports, the candidates are targeting voters in the West in a last-minute effort.

The Democratic candidates and some of their prominent supporters have been in and out of the state in recent days.

At a Los Angeles rally Sunday, Maria Shriver, the wife of California's Republican governor Arnold Schwarzenegger, endorsed Illinois senator Barack Obama. Her husband backs Republican candidate John McCain.

Shriver, a Democrat, is the niece of the late president John F. Kennedy and is the third prominent Kennedy to back Obama, after Caroline Kennedy Schlossberg and Senator Edward Kennedy endorsed him a week ago.

"The more I thought about it, I thought, you know, if Barack Obama was a state, he'd be California. I mean, think about it, think about it - diverse, open, smart, independent, bucks tradition, innovative, inspiring, dreamer, leader," she said.

The Kennedys, like many Democrats, are divided. Several other family members are backing New York Senator Hillary Clinton.

The independent Field Poll organization said Sunday that Clinton's lead in California has evaporated, and she is now in a dead heat here with Obama.

Among Republicans, Arizona Senator John McCain doubled a four-point lead from two weeks ago to lead former Massachusetts governor Mitt Romney by eight points in the state, or 32 to 24 percent. Former Arkansas governor Mike Huckabee trails at 13 percent.

As Californians make their choices Tuesday, they will be joined by voters in neighboring Arizona and New Mexico, and others in Colorado and the so-called inter-mountain states of Utah, Idaho and Montana. Alaskans will also hold both Republican and Democratic caucuses.

Political analyst Sherry Bebitch Jeffe says voters in the West are concerned with national issues, such as the economy and Iraq.

"There are also very specific issues, such as the environment, energy, water is a major issue in the West. Obviously, gasoline prices are of a critical concern in the West. But those issues that concern most Americans are those that also concern Westerners and Californians - the economy, Iraq, education, immigration, health care," she said.

She says there are really two different races under way. One is for the popular vote, the other is a hunt for delegates to the nominating conventions of the parties.

"And that will go on delegate by delegate, congressional district by congressional district. So even if, for example, [looking at] one of the two Democratic candidates, even if Barack Obama does not win the popular vote in California, he can come out with a significant number of delegates," Jeffee said.

Because of complicated rules for awarding delegates, she says one candidate could conceivably win the popular vote in a state like California, but the other could win the most delegates.

The campaigns and political organizations are working to get out the vote.

One grassroots group on the Democratic side was started by former presidential candidate Howard Dean, who is now chairman of the Democratic National Committee. Dean's brother, Jim, chairs the group Democracy for America, which has not endorsed a presidential candidate, but is urging Democrats to vote.

He says after a nominee emerges in the coming weeks or months, the focus will shift to November's general election, when voters across the country will choose the next president, and also vote for members of congress, and state and local officials.

"We'll certainly be helping the nominee, whoever that is, but it's going to be about getting everybody out there and getting everyone to talk to their family, friends and neighbors about how important this election is, both at the local, state, federal and certainly presidential level," he said.

Political analysts say interest in Super Tuesday is high in the West, and they expect a good voter turnout.