At a public hearing on Monday, MassHighway officials told Islanders to expect the temporary drawbridge across Lagoon Pond to stay in place for six years.

Stunned at the prospect, Islanders immediately urged the project engineers to finalize a design for the new drawbridge before beginning construction on a temporary replacement.

"The bridge is a vital component of our road system," said Mark London, executive director of the Martha's Vineyard Commission. "Our main concern is that decisions made regarding the temporary bridge would preclude some of the viable options for the permanent bridge."

"This is a major bridge between two large towns. The larger view is being taken by a lot of people," said Cape and Islands Rep. Eric T. Turkington. "This is an opportunity to improve a lot of problems, and you need to listen."

The three-hour hearing covered MassHighway's temporary bridge project, the first phase of a long-term plan to replace the 68-year-old Lagoon Pond drawbridge.

Although they are in the beginning stages of selecting a firm to design the permanent bridge, agency officials insist the existing bridge is in such poor shape they cannot delay its replacement.

About 70 people came to the hearing, held at the Katharine Cornell Theatre in Vineyard Haven. Selectmen from both Oak Bluffs and Vineyard Haven attended, along with town officials responsible for shellfish, harbor and water quality management.

Many came already wary of the $3.5 million proposal, and left unconvinced that their input had affected the project or its time line.

Construction on the temporary bridge could begin in spring 2005.

Plans call for a prefabricated, modular bridge with an 80-foot bascule tower - a device balanced so that when one end is lowered the other is raised, thus opening the bridge. The roadway would be 24 feet wide, with five-foot sidewalks on either side.

Despite MassHighway officials' attempts to focus discussion on the temporary drawbridge, Islanders repeatedly urged them to think comprehensively. Because of the hefty price tag for the temporary bridge, many asked if the money could be better spent nursing the existing bridge along while plunging ahead with plans for the permanent structure.

MassHighway officials said there is no time.

"The district has put $3 million into emergency repairs over the past three years," said bridge engineer Alexander Bardow. "Deck failure is a distinct possibility; deterioration is accelerating and a lot of the machinery is corroded. We don't know how long it will last."

Recent inspectors of the bridge - who assess it based on national standards - have rated the deck only a step above critical condition. The superstructure and substructure both rank as poor.

In addition, the bridge frequently moves on its piles, causing the drawspan to jam when it opens and closes.

"No matter what happens, if you want to get across the road, we have to put up a temporary bridge. Time is of the essence," said project manager Steve McLaughlin.

Both said that having the temporary bridge in place would allow them the necessary time - at least six years - to design, permit and build a permanent drawbridge. It also would allow time to consider fully how pond circulation and navigational safety might be improved.

Poor water quality has been documented in the Lagoon going back as far as 1987, and this July nearly four million healthy juvenile shellfish under culture at the Lagoon Pond hatchery died because of it.

Tisbury Waterways Inc. (TWI) is sponsoring a hydrographic study of the pond. The study - which will be finished by June - will take into account water depth, current speed and size and shape of the pond basin relative to the channel. The information then goes toward building a computerized circulation model that can predict the effect of dredging projects on the pond.

"Rather than having an idea about what might work, this is an opportunity to knowfactually," TWI president Melinda Loberg told officials at the hearing. "This is our one opportunity to get it right, and I urge you to slow down so you can incorporate this study into your planning" for the temporary bridge.

Tisbury harbor master Jay Wilbur spoke about the unsafe design of the existing channel. Boaters moving between the Lagoon and the outer harbor cannot see traffic coming because of the sharp hook of the channel. Siting the new bridge closer to Tisbury would allow for a straighter approach.

Islanders spent less time commenting on the actual design of the temporary bridge. The plan originally called for filling in part of the Oak Bluffs side of the Lagoon to create a base for the bridge footings, which many feared would reduce circulation in the ailing pond.

MassHighway now proposes to ground its pilings on either side of the wetlands and salt marshes - and arch over the sensitive areas using several smaller spans - to avoid a direct impact.

But the design adjustments did little to ease larger community concerns.

"I know your job is to take the bridge and fix it, but that's not all that we want," said Tisbury selectman Tom Pachico. "We want to see you take the time to do it right, not just pop something in there."

"What the community wants is a more comprehensive plan of where we are going to end up - not with the temporary bridge but with the permanent solution," said Tisbury selectman Tristan Israel.

He urged MassHighway officials to consider creative alternatives to both the temporary and permanent structure: "It may be that yours is the only solution, but we don't know that. All we know is it's going to be in there a long, long time."

Mr. Bardow said he doubted a tunnel under the channel would be a feasible alternative and listed several drawbacks, including:

* The existing soils would make it difficult to construct with the existing bridge still in service;

* The time line for tunnel permitting is significantly longer than for a bridge, and

* Ventilation, drainage and lighting would be problematic, and would preclude pedestrians and bicyclists from using the roadway.

Islanders were not convinced, however, and wanted MassHighway to crunch the numbers and prove their case.

On Tuesday MassHighway spokesman Jon Carlisle called the tunnel unfeasible from an engineering standpoint. He added: "It was a useful forum, and we heard loud and clear from the community about a number of concerns. We do want to support a design [for the temporary bridge] that would not preclude the future enhancement of the Lagoon."