Forget finding an Internet cafe. For less than what it costs to build a small library, city officials believe they can turn all 135 square miles of Philadelphia into the world's largest wireless Internet hot spot.

The ambitious plan under discussion would involve placing thousands of small transmitters around the city, probably atop lampposts. Each of these wireless hot spots would be capable of communicating with the WiFi network cards that come standard with many computers.

Once complete, the $10 million network would deliver broadband Internet almost anywhere radio waves can travel, including neighborhoods where high-speed Internet access is now rare.

The city would likely offer the service either for free or at costs far lower than the $35 to $60 a month charged for broadband delivered over telephone and cable TV lines, said the city's chief information officer, Dianah Neff.

"If you're out on your front porch with a laptop, you could dial in, register at no charge, and be able to access a high-speed connection," Neff said.

If the plan becomes a reality, Philadelphia would leap to the forefront of a growing number of cities already offering or considering a wireless broadband network for their residents, workers and guests.

Chaska, Minn., a suburb of Minneapolis, began offering citywide wireless Internet access this year for $16 a month. The signal covers about 13 square miles.

Cleveland has added about 4,000 wireless transmitters in its University Circle, Midtown and lakefront districts. The service is free for anyone who passes through those areas. At 2:20 p.m. Tuesday, 1,016 people were logged in to the system, said Lev Gonick, chief information officer at Case Western Reserve University, which is spearheading the project and paying for part of it.

"We like to say it should be like the air you breathe -- free and available everywhere," Gonick said. "We look at this like PBS or NPR. It should be a public resource."

But free, citywide Internet access would appear to pose a competitive threat to businesses such as phone carrier Verizon Communications Inc. and cable provider Comcast Corp. Both companies have invested heavily in upgrading their networks to provide high-speed Internet connections for a monthly fee.

A free service might also hurt Verizon's wireless business, which is spending $1 billion to upgrade its network with a technology that will enable speedier Web access for laptops and mobile phones.

John Yunker, an analyst with Byte Level Research, said those companies could face a serious challenge if cheap or free WiFi proliferates.

"When you see initiatives like Philadelphia's, you are conditioning people to expect free or very low-cost Internet service. And that is going to be a problem for providers who have built a business model around charging a fee," he said.

While business users might be willing to pay extra for reliability or national coverage, a free service might prove more than adequate for more recreational Web use, Yunker said.

As it stands, a typical WiFi transmitter such as those used in homes, coffee bars and airports is at least several times faster than the broadband connection provided by high-speed cable or DSL over a phone line.

And thanks to surging demand, the cost of those hot spots and WiFi computer cards has fallen sharply in recent years. At the same time, a glut of capacity on wired networks built during the technology boom has made it cheaper to deliver Web traffic to and from WiFi hot spots.

Neff, for example, estimated it would cost Philadelphia $1.5 million a year to maintain the system.

The main drawback to WiFi is that the signal travels only several hundred feet. But the "wireless mesh" technology being considered by Philadelphia and other cities essentially joins those individual hot spots into a network to provide service across entire neighborhoods.

Philadelphia Mayor John F. Street, who carries a wireless handheld computer everywhere he goes, appointed a 14-member committee last week to work out the specifics of his city's plan, including any fees or restrictions on its use.

Elsewhere, New York City officials are negotiating to sell six companies space for wireless transmitters on 18,000 lampposts for as much as $21.6 million annually.

Corpus Christi, Tex., has been experimenting with a system covering 20 square miles that would be used by government employees.

Vince Veneziani uses a wireless connection to access the Internet in a Philadelphia park. A city plan calls for a network of wireless transmitters.