Among the many things the Internet does with incredible efficiency is breed conspiracy theories.

So as the great network has evolved, concerns about whether the companies that control the Internet's pipes might one day discriminate among what Web sites you could see, or whose movies you could download, have often been dismissed as silly, impossible or both.

The response from network owners, particularly the cable-television companies that provide increasing percentages of high-speed Internet connections, has always been: "Is there evidence that we've ever done this?"

For the most part, no. But the concept of "network neutrality" has not just been a worry of the usual lineup of consumer groups and liberal Internet think tanks.

Large tech companies such as Amazon.com, Yahoo Inc. and Microsoft Corp. raised the alarm last year, asking the Federal Communications Commission to consider establishing principles that would help ensure that the Internet grows up as a place that allows basic consumer choice.

Their view is that the Internet is such a vital component of life that it should resemble, in a small but crucial way, the electrical grid. One can imagine the chaos if your power company could take money from Sony Corp. so that its appliances got a higher quality of juice -- and thus worked a tad better -- than those of Mitsubishi Corp.

The power system wasn't built that way, but high-speed Internet service providers have that very capability. Technology now exists that enables network operators to recognize the data packets that move across their systems, and to prioritize them. This is, in fact, how some universities are spotting and cracking down on music file-sharing over campus networks.

Would Internet service providers exercise that control? Some intriguing speculation came recently from the Yankee Group, a market research firm that services major corporations.

In a controversial report issued early this month, Yankee analysts looked at one of today's hottest technologies, voice service over the Internet, also known as VoIP. Specifically, the analysts were pessimistic that the biggest VoIP player today, New Jersey-based Vonage Corp., could survive once the cable and telephone companies that provide most broadband Internet connections jump into the VoIP game, as they are beginning to do.

Primarily, the analysts said, the Internet operators would effectively bundle VoIP with other offerings, making it hard for independents such as Vonage to compete. But the analysts also said this:

"It may seem like a dodgy competitive tactic, but broadband network providers could slow down Vonage's service. As subscribers increase their use of latency sensitive and graphic rich . . . traffic, broadband providers could give network precedence to their own revenue-generating services. Unless Vonage pays fees to the network provider, there is no reason the operator should not make the service a lower priority on the network."

This is a bit chilling to Vonage chief executive Jeffrey Citron.

"If that happens in this world, the value of the Internet would instantaneously be massively devalued," he said, because it could happen with any kind of content or application. Although Vonage has seen no actions to degrade its service in the United States, its engineers are suspicious about some complaints it has received from customers in Canada.

Citron said network operators might not choose to impede some services. They could achieve the same thing by having companies pay to have their content or services delivered faster, or first.

Yankee Group analyst Lindsay Schroth considers that reasonable. Why shouldn't the companies that built and run the Internet pipes feeding the home be able to capitalize on their investments? In her view, Internet service providers will begin to provide add-on services, such as higher speed movie downloads, or enhanced online gaming, for additional fees paid by consumers.

Link Hoewing, a Verizon Corp. vice president in charge of Internet policy, said he does not think consumers or businesses would tolerate active discrimination by ISPs. But he said providers need to be able to make money on services beyond the basic connection fee.

Citron said he hates government regulation in general, but this is one case where it might be needed. He said the government should spell out what constitutes a minimum level of broadband service. At least then, he said, Internet users could always receive a baseline level of service, and could pay more to upgrade if they wanted.

The cable industry's trade arm dismisses this as needless regulation, a solution in search of a problem. National Cable Television Association spokesman Brian Dietz said it is hardly in cable's interest to meddle with VoIP quality, because more VoIP users means more broadband customers.

And if customers don't like the Internet service they are getting on cable, they can switch to high-speed DSL from a phone company, he said.

AT&T, which also is jumping into the VoIP market, says it is taking the cable industry at its word that it will not discriminate. But the company is watching carefully and worries that the potential for mischief increases as the country increasingly moves toward a broadband duopoly of the large phone and cable operators.

At the FCC, Chairman Michael K. Powell has endorsed the notion of neutrality and challenged the industry to uphold it.

But no rules proceedings are in the works, pending a court case that could change the rules governing cable Internet service.

In the meantime, though, technology marches on.

.Com columnist Leslie Walker is away and her column will resume when she returns. Jonathan Krim can be reached at krimj@washpost.com.