The program, Citi Bike, was supposed to begin in July; it will not, but city officials will not say when it will.

Mayor Michael R. Bloomberg has attributed the delay to “software” problems, though officials have been unwilling to explain the issue in greater detail.

Dock stations for the bikes can be assembled quickly enough that an August kickoff remains possible, but no guarantees have been made.

And increasingly, some elected officials and members of the riding public appear befuddled by the city’s virtual silence in recent weeks, when many had hoped to be cycling already.

“I’ve been waiting for it for months,” said Ted Larkin, 45, a cyclist from Midtown who said he had been checking the program’s Web site frequently for details that never seemed to come. “If not from them, where can one find the information?”

The Transportation Department said last week that it was “working on the launch plan” and promised to update the public “as soon as we finalize all the details.”

When asked to clarify the software problems on Thursday, Seth Solomonow, a spokesman for the department, said, “All we’re saying is, refer to previous statements on this, including the mayor’s.”

A spokesman for Alison Cohen, the president of Alta Bicycle Share, which is operating the program, said Ms. Cohen was not available for interviews or comment. She has rarely spoken publicly in recent months, and Alta, when contacted last week about possible delays in the program, referred all questions to the Transportation Department.

Given little information, riders have searched for prospective tea leaves. Some have looked to the example of Chattanooga, Tenn., where an Alta-run bike-share program kicked off on Monday after months of software-related delays. Others have scoured the program’s Web site or Twitter feed, @CitibikeNYC, which has supplied evolving answers to New Yorkers about the start date in recent weeks. “Why so hush-hush?” one user asked on July 9. (He was told then to expect an August start date; more recently, the account has taken to informing riders only that “details are being finalized.”)

On Thursday, the Twitter feed offered that it was “never too early to start loving bicycles.” It directed followers to an image of an infant onesie — pink, with a bicycle on the front — available for $18 plus shipping.

Some elected officials have called for greater transparency. Councilman James Vacca, the chairman of the City Council’s Transportation Committee, said the delay itself was not a concern; it signaled a prudent approach to a sprawling project. But the city’s muted response to the delay, he said, was troubling.

“In this case certainly, many people have been kept out of the loop,” he said, including himself. “Has D.O.T. had communication issues? Yes, they have.”

Councilwoman Gale A. Brewer, who described herself as a friend of the department’s commissioner, Janette Sadik-Khan, said the delay had not caused a clamor for bike-sharing among her constituents. But, she said, the department should “be more honest” about what is causing the wait.

“I do think D.O.T. should tell us what the issues are,” she said, “because we would understand them.”

For months, details in the lead-up to the program, hailed as a potentially transformative initiative in the city’s transportation history and a crucial piece of the Bloomberg administration’s legacy, have been tightly guarded. After the city announced in May that Citigroup would be the program’s lead sponsor, a WNYC report suggested that the city had had difficulties securing private funds and had signed a contract with Citigroup far later than officials had hoped.

“We started a little bit late,” said Paul Steely White, the executive director of Transportation Alternatives, a rider advocacy group that has worked alongside the Transportation Department to promote the program. “It took a long time to find the private funding.”

But, Mr. White added, the city’s handling of the delay was not cause for alarm.

“No news is no news,” he said. “It’s a virtual certainty that these kinds of deadlines are always moved back.”

Indeed, Mr. Bloomberg has suggested that any anxiety over the start date is proof of the city’s enthusiasm for the program, an assessment many residents acknowledged as true. But this enthusiasm, some said, was reason enough for the city to keep the public informed.

“It would have been great to use for the summer,” said Katrina Tang, 27, a photographer from Estonia who said she was leaving the New York area in September. “Things do take a bit longer here.”

Mr. Larkin, who said he has ridden in the city since his childhood, compared the situation to that of a restaurant that has run out of a favorite dish: Diners prefer to know about the problem before they order, he said.

“Bad news,” he said, “should be delivered sooner rather than later.”