PORTLAND – During its 20-year history, the Land for Maine’s Future program has spent $72 million and helped conserve 445,000 acres of forests, farms, waterfronts and mountaintops through purchases and easements.

This year, voters will decide whether to authorize an additional $17 million in borrowing so that more land can come under state control.

The popular program was created in 1987 amid concern about development pressures that were turning forests and other open spaces into house lots. By a 2-1 ratio, voters gave a thumbs-up to the $35 million bond issue that kicked off the program.

“Four hundred thousand acres later … it has proved to be something that government has done that was just what people wanted,” said Pat McGowan, commissioner of Maine’s Department of Conservation, who will unveil the program’s latest project Tuesday near the Androscoggin River in Turner.

The program has seen a number of changes over the years, including an eight-year-old requirement that all projects raise matching contributions from other sources. Since then, every dollar in state money has been matched by more than $4 in federal, local or private donations, according to Tim Glidden, the program’s director.

Still, some supporters of the conservation fund say it has failed to keep pace with development pressures, and that the Legislature should be earmarking more money for land purchases and easements.

“All of the land is increasing in selling price at an incredible inflation rate, and opportunities to really protect some decent portions of Maine are being lost,” said Robert Cummings of Phippsburg, president of the Maine Appalachian Trail Land Trust. “It’s a wonderful program. It could have been much, much better.”

Although Maine broke new ground in establishing its land conservation program, many other states have taken similar steps during the past two decades. Some spend far more money, including New Jersey, which spends $100 million a year.

Some critics say the fund should be directing more spending toward southern Maine, where development pressure is strongest. More than half of the acres preserved through 2006 are in sparsely populated Piscataquis and Washington counties, accounting for more than one-third of the money.

“Land is cheaper up here, but how can you justify spending the majority of the money up here when in fact most of the need is in southern Maine?” said Jonathan Reisman, associate professor of economics and public policy at the University of Maine at Machias.

Reisman said the program appears to have shifted its focus recently to southern Maine, particularly York County. “I think it’s gotten a little better,” he said.