Campaign spending on a proposal to put a racetrack with slot machines in Westbrook or Saco exceeds $600,000, a figure that should continue to rise until voters go to the polls next week.

More than $500,000 of the expenditures listed in finance reports filed Wednesday were by two groups opposed to a racino: Maine Opportunities and CasinosNo!

Voters in Saco and Westbrook will decide Tuesday whether Scarborough Downs should be allowed to build a racino.

The two sides acknowledged that the $75 million to $125 million in annual profits a racino would produce are helping to fuel the flurry of spending. Finance reports show that the Downs’ partner, Penn National Gaming, has donated $150,000 to two pro-racino groups.

“Spending that amount of money on a campaign we think is a good investment for us and Scarborough Downs,” said Eric Schippers, spokesman for Penn National.

Voters statewide approved slot machines at Bangor Raceway and the Downs on Nov. 4, but Scarborough residents rejected slots in their town. The new law allows the racino to be within five miles of the racetrack’s location in 2002, but stipulates that local approval is needed by Dec. 31. Both Westbrook and Saco, which have suitable land within the five-mile limit, agreed to hold local referendums Tuesday.

Those decisions triggered a fierce one-month campaign involving the Downs, anti-racino advocates inside and outside the cities, and Maine Opportunities, a political action committee backed by Shawn Scott, who wants to operate a racino in Bangor.

Most of the money spent to date came from the coffers of groups that reported raising $804,000.

Finance reports, which state law requires six days before an election, show Maine Opportunities has spent the most money. It has spent $337,000 in cash and in-kind contributions for polling, staff and radio, television and newspaper ads.

Maine Opportunities reported raising $396,000, all of it from Waterways Investments of North Reddington Beach, Fla. The committee’s treasurer, Kathleen Newman, has said that Scott’s company Capital Seven is financing the committee.

The Downs and other opponents of Scott have said he is funding the Maine Opportunities campaign to eliminate competition in Maine.

Penn National’s two $150,000 donations went to Westbrook Citizens for Jobs and the Economy and Saco Citizens for Property Tax Relief. Most of the money has been spent on advertising. The Downs has spent $16,284 in cash and in-kind contributions.

CasinosNo!, which helped defeat a statewide referendum last month on a tribal casino, has raised $248,000 since Dec. 3 to fund its anti-racino campaign. Two local groups, Our City, No Slots! and No Slots Saco, which are working with CasinosNo!, also have raised money.