Edgartown is moving forward with a long-planned project to replace a World War II-era airplane hangar at Katama Airfield, despite concerns that the town may be getting a bad deal.

The selectmen endorsed the plan at their meeting Monday and are expected to sign an amended conservation restriction next week. The amendment clears the way for the project, which will double the size of the 1945 airport hangar.

Town counsel Ronald H. Rappaport told the selectmen again Monday that the deal comes at a price.

“What I said in the last meeting is . . . the town is giving up a lot to effectively double the size of a reasonably small hangar,” Mr. Rappaport said. “That’s over 21 acres of additional land of conservation restriction, with some uses being placed on it. People ought to take a deep breath and see what we’re giving up and if it’s worth it.”

Expanding the hangar triggered a complicated process that the town has been working on for the past several years. Among other things, it required an act of the state legislature to amend the conservation restriction at the 90-acre grass airfield, an environmentally sensitive area that was protected by the town, the state and The Nature Conservancy decades ago. The amendment also calls for placing 62.5 acres of land known as the Nickerson Property under the conservation restriction, converting 6,700 square feet of land at the airfield into a natural state, and transferring about 21 acres of town-owned land off Pennywise Path into conservation land with restricted use. The act also requires that The Nature Conservancy approve the hangar expansion.

The new restriction is a 17-page document.

Much of the legal wrangling has been with The Nature Conservancy, but Mr. Rappaport said Monday that the Conservancy has signed off on the deal and approved the hangar expansion.

Airport manager Mike Creato said the hangar project will be a benefit.

“The town sure has put a lot into preserving the airport and Katama Farm . . . and there’s a benefit to having a building that sort of cleans it up out there,” he said. “There’s a nice oasis. It’s a little messy and overridden, but I think it’s a worthwhile effort to make it a viable facility. It’s not without a pretty good return.”

Selectman Arthur Smadbeck said he backs the plan but wants guarantees.

“We’re all in favor of it . . . . What I don’t want to do is inadvertently obligate the town into something without a rock solid guarantee what we’re doing gets us what we’re trying to do,” he said.

The selectmen are expected to sign the amended conservation restriction at their meeting next week.

“I think we’re on our way hopefully,” said selectman and chairman of the board Margaret Serpa.

In a related move, the selectmen also voted to split the management duties of the airport and restaurant operations, and will issue a request for proposals. Mr. Creato plans to step down as manager.

In other business, the town will allow John Roberts, the owner of a commercial building at 11 North Water street, to put a dumpster on Mayhew Lane for a project to repair the building.

Town administrator Pamela Dolby reported that Edgartown, Oak Bluffs and Tisbury are applying for a state grant to pay the salary of an energy manager to oversee energy projects in all three towns.