Legalizing recreational use of marijuana in Washington, allowing same-sex marriage in Maine and permitting physician-assisted death in Massachusetts top a list of ballot measures in 38 states on Tuesday.

Marijuana, health, marriage and taxes are the dominant themes of the 176 statewide measures, according to a report by the Los Angeles-based Initiative & Referendum Institute at the University of Southern California.

“There are always a lot of social issues on the ballot,” said Jennie Bowser, a senior fellow at the Denver-based National Conference of State Legislatures. “This year, there’s a little bit of a twist with change in the same-sexmarriage issue and the prevalence of the marijuana issue without requiring the medical piece.”

Voters in Colorado, Washington and Oregon will decide whether to make their states the first to legalize the recreational use of marijuana, seeking to build on measures that allow it for medical purposes in one-third of states. Voters in Maine will consider whether to allow same-sex marriage, among four states taking up the issue and the first to consider legalization without initial action by a court or state lawmakers.

“Multistate issues can take on life and spread across the country if they meet with voter approval initially and reveal unexpected popular support for an issue,” according to the USC report. “For this reason, multistate issues are worth watching as possible leading indicators of national trends.”

Voters from San Francisco to Boston will consider proposals to require labeling of genetically modified food, defy President Barack Obama’s health care law and increase sales taxes to support schools. The 176 ballot measures outnumber the 159 in 2010 and 153 in 2008, according to USC.

Six states will consider ballot measures dealing with marijuana use for recreational or medical purposes. California, whose voters rejected a measure to legalize recreational use in 2010, was the first state to allow medical use in 1996. It’s now permitted in 17 states and the District of Columbia.

Massachusetts and Arkansas will consider legalizing the medical use of marijuana, while in Montana, voters will decide whether to affirm or reject a 2011 law that scaled back a 2004 initiative legalizing medical marijuana.

“At some point we’re going to reach a tipping point where the federal government has to cede to the states,” Allen St. Pierre, executive director of the National Organization for the Reform of Marijuana Laws, a Washington group that seeks legalization, said in a telephone interview. “These initiatives are one way to expedite that process.”

Besides Maine, three states will weigh marriage-related propositions. Maryland and Washington residents will decide whether to affirm state laws approved this year allowing same- sex marriage. Minnesota voters will consider whether to amend their constitution to define marriage as between one man and one woman.

To date, same-sex marriage has become legal only as a result of legislation or court rulings in New York, Iowa, Massachusetts, Connecticut, Vermont, New Hampshire and the District of Columbia. Obama this year became the first sitting president to endorse such marriages.

Voters in Alabama, Florida, Montana and Wyoming will consider propositions to prevent people from being required to get health insurance. The measures are aimed at blocking implementation of Obama’s health care law, which aims to create the largest expansion of coverage since Medicare in 1965.

In Massachusetts, voters will decide whether to allow physicians licensed there to prescribe medication to end the life of a terminally ill patient at that person’s request. The practice is legal in Washington, Oregon and Montana.

“The people of Massachusetts will have the same right as people in Oregon to know that if they are suffering unbearably they would be able to have a peaceful way out,” said Barbara Coombs Lee, president at Compassion & Choices, a Denver-based group that advocates for choices for the terminally ill.

U.S. ballot measures feature 31 tax-related proposals, including two competing initiatives in California aimed at raising money for schools. Proposition 30, offered by Gov. Jerry Brown, would temporarily boost the state sales tax to 7.5 percent from 7.25 percent and raise the levy on income starting at $250,000.

“Proposition 30 is money into the schools and colleges,” Brown said during a question-and-answer session after a speech Thursday in San Francisco. “It’s fair, it’s moral and represents the best in our California tradition, and it is critical to maintaining the California dream.”

Proposition 38, a proposal backed by Los Angeles attorney Molly Munger, would raise personal income taxes for 12 years. The rates would rise on a scale from 0.4 percent for people earning more than $7,316 a year to 2.2 percent for those making more than $2.5 million.

Munger, whose father Charles Munger is vice chairman of Berkshire Hathaway, has spent $44.1 million to support her plan, according to data released Oct. 26 by MapLight, a nonpartisan research organization based in Berkeley, Calif.

If both measures pass, the state constitution requires that the tax increases from the proposal that got the most “yes” votes would take effect.

California voters also will consider a proposal to abolish the death penalty, changing the maximum sentence to life without parole.

A California proposal to require labeling of genetically modified foods has drawn $45.6 million in contributions from companies opposing the measure. They include Monsanto, the world’s biggest seed producer; DuPont, the biggest U.S. chemical maker by sales; PepsiCo, the world’s largest snack-food maker, and Coca-Cola, according to MapLight.

“If you look at who’s funding the fight of an initiative, it very often reveals what the impact of the initiative will be,” Bowser said. “If they are spending money against it, there’s a good chance it’s going to be detrimental to their business.”