PORTLAND — Campaigns were making a final push Monday to snare undecided voters before an election that’ll decide the state’s next senator and whether gay marriage becomes legal in Maine. Also on the ballot are U.S. House and legislative races and $76 million worth of state bonds, in addition to local races.

In the U.S. Senate race, Republican Charlie Summers started his day in Presque Isle while independent Angus King wrapped up his three-day bus tour. Democrat Cynthia Dill visited Bath Iron Works but took time at midday to teach a civics class at Southern Maine Community College.

Supporters and opponents of the gay marriage referendum continued working the phones, knocking on doors and waving signs on street corners to bolster their causes.

Gay marriage supporters enlisted an airplane to circle downtown Portland, pulling a banner encouraging residents to support same-sex marriage at the polls on Tuesday.

Many Maine residents were just ready for the election to be over because of the overwhelming level of TV and radio advertising made possible by the Supreme Court’s Citizen United ruling, which allowed so-called super PACs to spend unlimited amounts of money on behalf of candidates or issues.

“Because of Citizens United and the staggering amount of capital, the propaganda machine isn’t going to stop,” said Gil Helmick, a frustrated voter in Portland.

Super PACs have spent millions of dollars in Maine, most of it in the Senate race, in which Republicans were trying to hang onto the seat vacated by Sen. Olympia Snowe.

Pre-election polls gave King a solid advantage despite months of attack ads targeting his business dealings and his fiscal management of the state as governor from 1995-2003.

King said the attacks were continuing in the form of a misleading robocall Monday as he wrapped up his bus tour with a rally outside his campaign headquarters in Brunswick. The robocall from Georgia-based Safe Nation PAC urged progressives to reject King because he “opposes marriage equality.”

“This robocall is the worst case of political sleaziness,” said Crystal Canney, King’s spokeswoman. She said King has long supported gay marriage “and has been on the record for years.”

A spokesman for the PAC said the phone calls referred to questions whether King supports repealing the federal Defense of Marriage Act. Canney said Monday that King supports repealing the law.

Both congressional races were contested with Democratic Reps. Chellie Pingree and Mike Michaud facing challenges by Republicans Jon Courtney and Kevin Raye in their respective races.

Mainers also will decide on a $76 million bond package, including $51.5 million for transportation projects, $11.3 million for capital improvements for universities and community colleges; $7.9 million for public drinking water and wastewater treatment facilities; and $5 million to buy land and conservation easements.

The number of absentee ballots issued by the secretary of state’s office was far fewer than four years ago, but that doesn’t necessarily translate to lower overall voter turnout, officials said.

A total of 188,180 ballots were requested as of Thursday’s deadline and more than 150,000 were returned. The numbers are far less than in 2008, when 238,940 votes were cast via absentee ballots.

State election officials predicted a turnout of 65 percent to 75 percent of the state’s voting population. In 2008, 70 percent of the state’s voting-age residents cast tallies.