SAN FRANCISCO — Internet entrepreneurs climb on stage at technology conferences and praise a world in which everyone is perpetually connected to the Web.

But down in the audience, where people are busy typing and transmitting this wisdom, getting a Wi-Fi connection is often downright impossible.

"I've been to 50 events where the organizer gets on stage and says, 'It will work,' " said Jason Calacanis, chief executive of Mahalo, a Web search company. "It never does."

Last month in San Francisco at the Web 2.0 Summit, where about 1,000 people heard such luminaries as Mark Zuckerberg of Facebook, Julius Genachowski, chairman of the Federal Communications Commission, and Eric E. Schmidtof Google talk about the digital future, the Wi-Fi slowed or stalled at times.

Earlier this year, Steven P. Jobs, Apple's chief executive, had to ask the audience at his company's developer conference to turn off their laptops and phones after his introduction of the iPhone 4 was derailed because of an overloaded Wi-Fi network.

And few of Silicon Valley's technorati seem willing to forget one of the biggest Wi-Fi breakdowns, on the opening day of a conference in 2008 co-hosted by the technology blog TechCrunch. It left much of the audience steaming over the lack of Internet access. The next morning, the organizers — who included Mr. Calacanis — clambered onto the stage to apologize and announce that they had fired the company that installed the Wi-Fi.

Technology conferences are like revival meetings for entrepreneurs, deal makers and the digitally obsessed. Attendees compulsively blog, e-mail, text and send photos and video from their seats.

Some go so far as to watch a webcast of the event on their laptops rather than look up at the real thing right in front of them. Nearly all conferences make free Wi-Fi available to keep the crowd feeling connected and productive.

The problem is that Wi-Fi was never intended for large halls and thousands of people, many of them bristling with an arsenal of laptops, iPhones and iPads. Mr. Calacanis went to the extreme at the Web 2.0 Summit by bringing six devices to get online — a laptop, two smartphones and three wireless routers.

He explained — while writing e-mails on his laptop — that as a chief executive and investor, he needed dependable Internet access at all times. "You've still got to work," Mr. Calacanis said.

Wi-Fi is meant for homes and other small spaces with more modest Internet demands, says Ernie Mariette, founder of Mariette Systems, which installs conference Wi-Fi. "You're asking a technology to operate beyond its capability."

Conference organizers and the Wi-Fi specialists they hire often fail to provide enough bandwidth. Many depend on the infrastructure that the hotels or convention centers hosting their events already have in place.

Companies that install Wi-Fi networks sometimes have only a day to set up their equipment in a hall and then test it. They must plan not only for the number of attendees, but also the size and shape of the room, along with how Wi-Fi signals reflect from walls and are absorbed by the audience.

"Every space is different and every crowd is different," Mr. Mariette said.

What is good enough for a convention of podiatrists is woefully inadequate for Silicon Valley's connected set.

"I've been to health care conferences where no one brings a laptop," said Ross Mayfield, president of the business software company Socialtext and a technology conference regular.

Technology conferences are an anomaly. Some regulars joke, perhaps accurately, that the events are host to more Internet devices per square foot than anywhere in the world. All too often, the network freezes after becoming overwhelmed with all the nonstop streaming, downloading and social networking.

That was what happened this year at the RailsConf, a software conference in Baltimore, when attendees caused Wi-Fi gridlock by tuning in to a webcast of an unrelated event across the country. Nearly everyone, it turned out, wanted to watch Apple's live unveiling of the iPhone 4, the very one that fell victim to a Wi-Fi crash.

Adding more Wi-Fi access points does not necessarily fix the problem, Mr. Mariette said. In fact, doing so may make the situation worse by creating more interference.

To avoid Wi-Fi gridlock, conference organizers sometimes ask attendees to turn off electronics they are not using and to refrain from downloading big files. Cooperation is generally mixed, however.

Last year, an attendee at Web 2.0 Expo in New York was so desperate to get online that he offered to pay Oren Michels, chief executive of Mashery, a Web services company, to share his mobile Internet connection. MiFi, as the device is called, enables users to create mini-Internet hot spots using a mobile carrier's network, not conference Wi-Fi.

"He said, 'Can I give you 20 bucks for access?' " Mr. Michels recalled. "It was just some random person sitting next to me."

Even if Wi-Fi devices are not connected to the network, they constantly emit signals that create background noise, sometimes until it becomes impossible to get online. IPhones and most BlackBerrys, along with certain laptops, are more susceptible than other devices because they operate on 2.4 GHz, a part of the spectrum that offers only three channels.

The Wi-Fi curse also extends to tech industry press conferences. Google, for instance, once held a press day at its headquarters in Mountain View, Calif., during which the Wi-Fi failed for several hours, although it was restored during the event's final minutes. The flub did not exactly build confidence that Google and its partner, EarthLink, could deliver on their plans — since abandoned — to blanket San Francisco with free Wi-Fi