NEW YORK - Although it has already taken nearly four decades to get this far in building the Internet, some university researchers with the federal government's blessing want to scrap all that and start over.

The idea may seem unthinkable, even absurd, but many believe a "clean slate" approach is the only way to truly address security, mobility and other challenges that have cropped up since UCLA professor Leonard Kleinrock helped supervise the first exchange of meaningless test data between two machines on Sept. 2, 1969.

The Internet "works well in many situations but was designed for completely different assumptions," said Dipankar Raychaudhuri, a Rutgers University professor overseeing three clean-slate projects. "It's sort of a miracle that it continues to work well today."

No longer constrained by slow connections and computer processors and high costs for storage, researchers say the time has come to rethink the Internet's underlying architecture, a move that could mean replacing networking equipment and rewriting software on computers to better channel future traffic over the existing pipes.

Even Vinton Cerf, one of the Internet's founding fathers as co-developer of the key communications techniques, said the exercise was "generally healthy" because the current technology "does not satisfy all needs."

One challenge in any reconstruction, though, will be balancing the interests of various constituencies. The first time around, researchers were able to toil away in their labs quietly. Industry is playing a bigger role this time, and law enforcement is bound to make its needs for wiretapping known.

There's no evidence they are meddling yet, but once any research looks promising, "a number of people (will) want to be in the drawing room," said Jonathan Zittrain, a law professor affiliated with Oxford and Harvard universities. "They'll be wearing coats and ties and spilling out of the venue."

The National Science Foundation wants to build an experimental research network known as the Global Environment for Network Innovations, or GENI, and is funding several projects at universities and elsewhere through Future Internet Network Design, or FIND.

Rutgers, Stanford, Princeton, Carnegie Mellon and the Massachusetts Institute of Technology are among the universities pursuing individual projects. Other government agencies, including the Defense Department, have also been exploring the concept.

A new network could run parallel with the current Internet and eventually replace it, or perhaps aspects of the research could go into a major overhaul of the existing architecture.

These clean-slate efforts are still in their early stages, though, and aren't expected to bear fruit for another 10 or 15 years — assuming Congress comes through with funding.

Guru Parulkar, who will become executive director of Stanford's initiative after heading NSF's clean-slate programs, estimated that GENI alone could cost $350 million, while government, university and industry spending on the individual projects could collectively reach $300 million. Spending so far has been in the tens of millions of dollars.

And it could take billions of dollars to replace all the software and hardware deep in the legacy systems.

Of course, a key question is how to make any transition — and researchers are largely punting for now.

"Let's try to define where we think we should end up, what we think the Internet should look like in 15 years' time, and only then would we decide the path," McKeown said. "We acknowledge it's going to be really hard but I think it will be a mistake to be deterred by that."