University of Washington researchers are worried that the proposed light-rail route through the University District won't be light enough.

With millions of dollars of research at stake, including work by Nobel Prize-winning physicist Hans Dehmelt, they worry that the rattle and hum of passing trains will throw off their ultra-fine measurements of electrons and electromagnetic fields.

"Precision measurements are at the corner of this department," said Steve Ellis, chairman of the UW physics department. "Whenever you bring in electromagnetic fields or vibrations, you threaten the future of that."

But Sound Transit officials worry that changes in the proposed route, announced last month, will delay the $2 billion project and cost it tens of millions of dollars in federal money.

"They are asking for us to consider some fairly significant changes in routing," said Denny Fleenor, a spokesman for Sound Transit "It's sort of a major change late in the game."

As planned, trains on the 24-mile North Seattle-to-SeaTac route would run just west of 15th Avenue Northeast. That would be 100 feet west and in a tunnel some 200 feet below the Physics/Astronomy building on Northeast Pacific Street.

The building, built for $65 million in 1992, features nonmetallic laboratories - metal throws off electromagnetic measurements - and work areas isolated from student traffic and supported to avoid vibrations from the building.

That's important when a researcher like Dehmelt traps an electron in an electromagnetic field and measures its properties with other electromagnetic fields, said Ellis. The work is so delicate that it can easily be thrown off by the electrical impulses from a train, he said.

"Then he won't measure the properties of an electron," Ellis said. "He measures combined properties of the electron and Sound Transit. And he doesn't want that."

University officials contend vibrations also affect work in the planned Life Sciences buildings involving atomic force microscopes that look at the nano-scale, or billionths of a meter. The Life Sciences buildings will be even closer to the train route.

University officials have proposed ways of altering the train's electrical systems to dramatically reduce the effect of their electromagnetic fields. But when it comes to dampening vibrations, said Ellis, "it's likely that distance is the only true and sure mitigation."

Still, the severity of those vibrations is unclear. Ellis worries that Sound Transit is pressing on with plans for the light rail and a Northeast 45th Street station without learning more about its effects.

Sound Transit workers tried estimating the effect of vibrations by studying freight trains in Everett and the soil around the university. The results were inconclusive. Now Sound Transit plans to study vibrations in a 260-foot tunnel in Portland that is the deepest in North America.

The transit authority hopes to finish the tests in April, Fleenor said. It has until August to complete its final environmental-impact statement, followed by more public comment before the Sound Transit Board chooses a final route at the end of the year.