ATTLEBORO - More than 100 acres owned by LaSalette Shrine off Park Street would become a "sanctuary for people and wildlife" under a blueprint announced jointly by LaSalette, Mayor Kevin Dumas, the Attleboro Land Trust and the Massachusetts Audubon Society.

The plan, which includes a conservation restriction on a large parcel at the rear of the shrine property, would require the cooperation of several public and private entities and be supported by a proposed $500,000 state grant and additional, privately-raised funds.

The land would stay in the hands of LaSalette, but remain undeveloped and be managed by the Massachusetts Audubon Society, which would administer programs and upgrade the property with parking, trails and a boardwalk and pondside platform.

Dumas unveiled the proposal at Tuesday's city council meeting, along with officials from Audubon and the Land Trust.

The mayor called the area behind the existing national religious shrine a "beautiful, pristine area" that would provide future opportunities for nature study, walking and contemplation.

The plan for the creation of the nature center will be referred to committee, which in turn will make a recommendation to the city council. Also appearing on behalf of the proposal Tuesday were Audubon Oak Knoll Sanctuary Director Sarah Slack, Audubon official Charles Wyman and Attleboro Land Trust Vice President Glenn Weidner.

Proponents stressed that the plan would involve no direct costs to the city, with money to be raised through a combination of state grants and contributions from private foundations.

The creation of the nature sanctuary would benefit the shrine and retreat center by attracting additional visitors and further the LaSalette mission of "reconciliation" between man and nature, as well as man and God, said the Rev. Roger Plante, a former retreat center director, who along with LaSalette Finance Administrator Michael O'Brien helped devise the plan.

"In today's world, you need oasises like this more than ever before," said Plante, who added that the preserve would keep in place habitats for a wide range of animals and provide a contemplative atmosphere for people seeking recreation or spiritual renewal.

"One complements the other," he said.

Plante noted that Pope Benedict XVI in one of his messages cited respect for nature and ecology, along with reverence for humanity, as essential to peace.

The project also falls within the LaSalette mission as stated in a 2006 policy initiative calling on its congregation to assist groups working to conserve Earth's resources and to "protect the integrity of creation."

The LaSalette Missionaries purchased the former Attleboro Sanitarium property in 1942 and established a monastery and national shrine to an apparition of the Virgin Mary to two French children in 1846.

The site has 23 resident priestly brothers, an active retreat center, a shrine church, gift shop and support buildings, all located on about 60 acres lining Park Street. The parcel being proposed as a nature preserve is at the rear of the LaSalette Shrine campus, and abuts city-owned land used for two schools, as well as a privately-owned parcel off Handy Street.

LaSalette, which will continue operating the shrine and its associated buildings, is constructing a large welcome center that will include a 600-seat theater.

Don LeStage, president of the Land Trust, said establishing the 110-acre nature preserve would solidify a 600-plus acre swath of green straddling Park Street only a short distance from downtown Attleboro. In addition, the city owns 260 acres of largely undeveloped land, which includes the sites for Hyman Fine and Wamsutta middle schools. The adjacent Locust Valley Country Club accounts for another 208 acres.

Other green sites in the immediate area include the Land Trust-owned Coleman Reservation and Vaughan Memorial Forest and the Massachusetts Audubon Society's Oak Knoll Wildlife Sanctuary, with a combined total of 149 acres.

The proposal to create a conservation restriction on the land, which was approved by LaSalette officials last October, represents the second major effort to preserve the land as an area for nature and contemplation.

The first, dating back more than 30 years, envisioned turning the land into a landscaped park for spiritual reflection. However that plan, developed by community leaders, including landscape designer and conservationist David Perry, was rejected by LaSalette officials.

The latest strategy stems from a 2005 conference on conserving religious lands, which provided a catalyst for creating the project, Plante said. The Audubon Society and the Crystal Spring Center for Earth Learning in Plainville, which works with religious groups to foster land preservation, played major roles in providing research and technical support, he said.

A complex web of agreements, relationships and grants would be required for the transformation of the 110-acre religious site into a nature preserve.

Although the land would continue to be owned by LaSalette, it would be managed by Massachusetts Audubon. Audubon would also provide educational programs and install trails and other improvements. The conservation restriction, meanwhile, would be held by the city and the Attleboro Land Trust.

Funds to purchase the conservation restriction would come from a $500,000 state self-help grant to be applied for by the city and $235,000 in additional funds that would be raised locally through individual contributions and charitable foundations.

The money would not be held by LaSalette, but would be passed through to the Massachusetts Audubon Society to pay for improvements and create a small endowment for future maintenance.

LaSalette officials estimate the land, which contains wetlands as well as higher elevations suitable for construction, is valued at $2.5 million to $3 million. If the conservation restriction is put in place, no future development would be allowed on the property.

The conservation restriction would remain in place permanently, Plante said. If the LaSalette Missionaries ever sell the shrine site, the agreement calls for them to convey land covered by the conservation restriction to the Audubon Society.

There are currently no plans under way or envisioned in the future to dispose of the religious site, which attracts tens of thousands of visitors annually for retreats and an annual Christmas lighting festival, he said.

LeStage said the addition of the nature sanctuary would greatly enhance one of Attleboro's most unusual assets: a huge expanse of unspoiled land in the heart of the city available for walking or observing nature.

According to a 2006 survey of the property by Audubon conservation scientist Robert Buchsbaum, the land hosts a number of wild animal species, including white-tailed deer and fisher, along with a variety of native and migratory birds.

The site is considered a priority habitat for rare species by the Massachusetts Natural Heritage and Endangered Species Program because of the presence of the spotted turtle in the area.

Five potential vernal pools and a natural spring have been identified on the LaSalette land, and plant life includes spicebush and 100-foot, old-growth trees, a rarity in a suburban environment.

The site has been identified as part of the Massachusetts BioMap Core Habitat, and within the top 10 percent of all land in Massachusetts considered priorities for preservation.

If city officials approve, the initial application for the $500,000 grant would go out by next July. Fundraisers are targeting private donors for the additional $235,000.

Weidner said those who are interested in learning more about the project or would like to make a contribution can contact the Attleboro Land Trust through its Web site, www.attleborolandtrust.org.