The rebuilding of the Storrow Drive tunnel - a controversial project that threatens to disrupt life in one of Boston's most beloved riverside parks - is being postponed.

The commissioner of Conservation and Recreation, who controls the rebuilding of the 55-year-old decaying tunnel, has delayed filing a key environmental impact report that would move the project forward. And the lead engineering consultant on the project has told associates to "please hold off on doing any more work on the project unless we specifically ask for something," according to portions of a memo e-mailed to a Globe reporter.

The question for residents who use the Charles River Esplanade walkways and bike paths and the 100,000 commuters who travel the tunnel daily is: How long? Officials do not want to commit to a timetable, even as they acknowledge that the roadway will need millions of dollars in interim repairs.

Richard K. Sullivan Jr., commissioner of conservation and recreation, acknowledged in a telephone interview yesterday that his agency had missed a self-imposed Oct. 1 deadline to file what is known as a Draft Environmental Impact Report with the state. The report is a first step toward designing the reconstruction, and the project cannot go forward until the plan is submitted and reviewed.

"I've said before that I wasn't going to rush to a date to file a DEIR until we had as much information as we could have and we could gather public input," Sullivan said yesterday.

State Representative Martha M. Walz, a Democrat who represents the Back Bay neighborhood, said that "in prior postponements there was always a target date."

"Any significant delay in the project is a cause of concern," she said.

Previous timetables had pegged the start of construction as 2010 at the earliest, she said. But she now fears that delaying the environmental review process will push the project start until at least 2011, possibly later.

"It's unclear to me why we're going to spend millions of dollars in temporary repairs," Walz said. "A long delay just increases the safety risk, increases the need for temporary work, and just delays a decision."

Walz, like many of the residents in her district, opposes a leading construction plan that would place a temporary roadway directly on the Esplanade, paving a road in an area that is popular for strolling and dog-walking.

Walz agreed with Sullivan that the tunnel does not pose an immediate danger to cars or pedestrians.

Sullivan said "there's absolutely going to have to be movement." But he also suggested that intense public protest over the rebuilding plans has contributed to the delay.

"I think we're going to have to take a look at Storrow as it relates to the entire [Charles River] basin," he said, pointing out that aging roads and bridges in the area all need significant structural work. "This is not a project that can just be done in a vacuum.

"All the options have been placed out there . . . Nothing has been taken off the table."

In the meantime, the cost of temporary fixes on Storrow continues to rise. Last week, workers began $450,000 in drainage repairs, Sullivan said. Sullivan said that over the next several years, he is expecting to spend $6 million to $10 million on major interim structural work.

Long-term solutions are estimated to cost $40 million to $65 million.

"There will ultimately have to be a larger project - replacement or otherwise," he said.

The recent spate of delays were first reported in yesterday's Boston Courant.

An Oct. 23 memo from lead engineer Mike McCall said the "permanent rehabilitation project will be postponed indefinitely," and instructed members of the design team to "archive your incomplete work so you can pick up again if ever asked to do so."

Elliott Laffer, who chairs the Storrow Drive Transportation Advisory Committee, said he hopes the delays will not be extensive.

"We'd like them to figure out what they're going to do," he said.

Anna Badkhen of the Globe staff contributed to this report.