DETROIT — A nonprofit group's plan to transform what remains of old Tiger Stadium into a commercial and educational center has received preliminary approval from the city of Detroit.

The Economic Development Corp. granted approval to the project's budget and plan in a letter dated Friday to Thomas Linn, president of the Old Tiger Stadium Conservancy.

After months of uncertainty about the prospects for saving part of the historic ballpark, "now there is a clear sense of 'yes, we can,'" said conservancy secretary Gary Gillette on Tuesday. "We have demonstrated that we have a clear plan, we have demonstrated that we are working on the practical components, we have demonstrated that we are working with the community ... This is a huge step forward."

But a greater challenge is still to come — the conservancy faces a March 1 deadline to show it can provide an estimated $27 million to pay for the project.

And city officials still have reservations, with the letter to Linn noting that "EDC staff is not fully in agreement with all the assumptions contained in the Plan and Budget."

"We recognize that the Conservancy has taken on a tremendous challenge, and it has presented us with a very aggressive financial plan. Nevertheless, we felt it appropriate to give the Conservancy an opportunity to continue moving forward toward its next milepost," said Brian Holdwick, vice president of business and financial services at the Detroit Economic Growth Corp., which staffs the EDC, in a written statement.

Tiger Stadium was built in 1912 as Navin Field and later was known as Briggs Stadium. The Detroit Tigers played thousands of games there before moving to nearby Comerica Park after the 1999 season.

The historic ballpark has stood vacant for almost a decade. Demolition began last summer but a wedge extending from dugout to dugout was left standing as the debate over preservation continued.

The conservancy has ambitious plans for the remaining portion of the stadium, including restoring the ballpark to its pre-1978 green paint job.

The Tigers' old clubhouse and the broadcast booth area would be preserved as exhibit space for baseball and sports artifacts. Retail stores and restaurants are planned for the ballpark's main level as well as 20,000 square feet of leasable office space in the upper deck.

The field itself would be used for youth baseball and other activities.

After a closer evaluation of the project's costs, the price tag has almost doubled from the figure of $15 million or $16 million presented last year, Gillette said.

According to the group, a recent change in state law permits the conservancy to receive federal and state historic tax credits totaling 40 percent of the project's costs, contingent on the project receiving some federal funding. A $4 million earmark was approved by a Senate committee last year but has been held up by a federal budget stalemate.

Additional funding for the project and predevelopment costs such as architects' fees could come from individual donations, foundation support, loans, other state and federal tax credits and possibly a slice of President Barack Obama's proposed stimulus package, according to Gillette.

"We are certainly making tremendous progress and I think things are falling into place beautifully right now," Gillette said.