Pima County will save nearly 260,000 acres through developer land donations and outright purchases over the next 50 years to meet federal Endangered Species Act requirements, a new county report said Wednesday.

But the county's habitat conservation plan, now in the works for seven years, still faces key question marks about short- and long-term financing. The county doesn't know the cost to acquire all the land needed, or where money will come from to make sure it's properly managed.

The county is already way ahead in its land-buying march to compliance with the federal law for the first 10 years of that period, according to the new report.

It has acquired more than 30,000 acres since 1999 with its two big open-space bond issues and other sources. It plans to purchase or obtain development rights to a total of 53,000 acres over that first 10 years, which suggests that the county will be ahead of the game by then.

In fact, County Administrator Chuck Huckelberry said in an introduction to the report that the county has already made its most difficult and important decisions regarding conservation. One was passage of a $174 million open-space bond issue in 2004. The other: the county's 2001 creation of a system of guidelines in which developers who get rezonings agree to set aside up to 95 percent of their environmentally sensitive land.

Huckelberry calls the habitat conservation plan "an insurance policy, intended to create long-term economic stability as we grow in a way that adds to our quality of life."

The new report, more than 2 inches thick, is the third and most detailed draft in as many years of the proposed county habitat plan. County officials hope the Fish and Wildlife Service will approve it this year.

The plan doesn't spell out a total cost of land buying over 50 years because, "There's no way to project beyond 10 to 20 years what land values will be," said Paul Fromer, a San Diego environmental consultant who helped prepare the plan.

The county proposes to have the land-saving plan reviewed every 10 years, to see if adjustments are needed to meet the plan's long-term conservation goals, Fromer said.

The more immediate question is how to pay for a detailed program to maintain and manage the land it buys, and to monitor the health of 35 vulnerable species of fish, birds, plants, mammals, reptiles and amphibians it hopes the plan will protect. The report pegs the potential annual cost of this program at more than $4 million annually after 10 years.

Officials are still discussing and analyzing various ways of raising the money, the new report said. Fromer said he would like to see a formal proposal when the Fish and Wildlife Service releases an environmental impact statement on the plan later this year.

Last year, a county advisory committee representing numerous interest groups recommended several fund-raising plans. None have yet won Huckelberry's support. They included proposed building-permit fees and creation of a long-term endowment fund.

The committee also recommended that county and city of Tucson officials consider creating a joint habitat conservation plan. That's in part because the city government has broader legal authority to come up with fund-raising tools than county government.

City Manager Mike Hein wrote the committee last October that the timing of the two plans could be problematic, because the city won't release its final draft for several more years. But he said the city would be glad to integrate the two plans in a matter recognizing the differences between urban and suburban issues.

Huckelberry wrote in November that any local government can join the county's effort if it agrees to meet the county's conservation standards and principles.

On Wednesday, Fromer said he thinks a joint plan is a possibility, although he said it's not clear whether the governments would do a combined plan or work on a parallel course on separate plans.

"It would be good idea not just to generate money for long-term management and monitoring of the preserve, but to give Tucson the assurances it wants for reasonable growth," said David Hogan, an advisory committee member and urban wildlands coordinator for the Center for Biological Diversity. "The county has already done the scientific work on the plan. Tucson doesn't have to reinvent the wheel.''

Realtor Bill Arnold and developer Chris Sheafe, who are also committee members, said they weren't concerned that the financing plan hadn't materialized.

"I think it's important that the plan be functional and that it be financially practical, and that's going to take some work," Sheafe said.

All that's ultimately important is that the financing plan eventually appear, said Arnold, adding, "I think it would be better to know what those mechanisms are up front, but … we have to deal with what we've got."

Key elements of Pima County's Proposed Habitat Conservation Plan

● Developers would set aside 122,845 acres of environmentally sensitive land over the next 50 years when they get rezonings of similar land.

● The county would buy or otherwise protect an additional 135,800 acres of environmentally sensitive land.

● In return, developers would be able to build on 72,937 other acres — 44,650 inside the county's Conservation Lands System of sensitive lands and 28,287 outside it.

● Thirty-five vulnerable species would be protected under the plan, down from 55 originally.

● The county will use 8,379 acre-feet of effluent to help restore streamside vegetation along the Santa Cruz and Rillito rivers and in Cienega Creek, the Cañada del Oro and Big Wash, among other riparian areas.

● The county will establish a work group to coordinate efforts to identify, map, control and eradicate invasive plants and take other steps to run a program to combat the spread of non-native species.