State election officials announced Wednesday that an initiative to legalize marijuana will be on the November ballot, triggering what will likely be an expensive, divisive and much-watched campaign to decide whether California will again lead the nation in softening drug laws.

Los Angeles County election officials Wednesday turned in their official estimate of the number of valid signatures, putting the statewide figure above the 433,971 needed for the measure to make the ballot. The county, where one-fifth of the signatures were collected, was the last to report its count, filing just before 5 p.m.

Polls have indicated that a majority of voters in California want marijuana legalized, but the margin is not enough to ensure the initiative will win. Two years ago, opponents defeated an attempt to relax the state's drug laws despite being outspent. "It's always easier for people to say no than to say yes for an initiative," said Mark Baldassare, the pollster for the Public Policy Institute of California. "Generally, all it takes is for people to find one reason to say no."

The initiative would allow adults 21 or older to possess up to an ounce for personal use. Possession of an ounce or less has been a misdemeanor with a $100 fine since 1975, when Atty. Gen. Jerry Brown, who was then governor, signed a law that reduced tough marijuana penalties that had allowed judges to impose 10-year sentences. Legalization supporters note that misdemeanor arrests have risen dramatically in California in the last two decades. The initiative would also allow adults to grow up to 25 square feet of marijuana per residence or parcel.