BOULDER, Colo. (AP) _ One of the strongest geomagnetic storms since 1976 disrupted communications across much of the northern United States on Saturday, a spokesman at the National Oceanic and Atmospheric Administration said.

The disruption of the Earth's normal magnetic field meant problems for satellites, radios and aircraft, but also meant a ''northern lights'' display much farther south than usual, a spokesman at NOAA's Space Environment Services Center said.

The spokesman, Bill Brennan, said this week's storms - the worst of which started at midafternoon Saturday and was expected to last 24 hours - were linked to a series of powerful solar flares this week.

In a geomagnetic storm, a surge of energy from the sun enters the earth's magnetic field and causes all sorts of electrical interferences.

While such a phenomenon can also mean difficulties with power distribution and phone lines, engineers monitoring such systems can make adjustments to deal with the problems, Brennan said.

The aurora borealis from Saturday's storm was expected to be overhead in the latitude that encompasses both New York and Chicago, Brennan said.

In fact, the storm's intensity meant that ''if the skies are clear, you will be able to see an aurora from almost anyplace in the United States,'' Brennan said. Unfortunately, a storm system meant cloud cover over much of country, he added.

''We're told that above 40 degrees latitude radio communications people are experiencing real problems,'' Brennan said.

The atmosphere becomes denser in such a storm and causes satellites to stray from perfect orbits. Adjustments must be made to continue the same level of service from the satellites, Brennan said.

Geomagnetic storms also can disturb the navigation systems of homing pigeons, which navigate by the earth's magnetic field, Brennan said.