What may have been the biggest solar flare in 25 years yesterday distrupted radio traffic between Miami and commercial airliners coming from Latin America and knocked out for three hours ship-to-shore communications from Boston to New Orleans.

The flare erupted at 8:08 a.m. EST and lasted for almost three hours, covering an area of the sun's upper lefthand quadrant 50 times the size of the earth's surface.

The flare produced more X-rays than any flare in four years, more visual change than any flare in 25 years and more radio emissions than any flare since flares were first scientifically recorded in 1946.

"Our switchboard's been lit up ever since early this morning," said Gary Heckman, chief on the Solar Forecast Center at the National Center for Atmospheric Research in Boulder, Colo. "This was one of the biggest and most complex flares we've seen in a long time."

Little if at all understood, a solar flare erupts when the magnetic energy stored just below the surface of the sun changes its form and is released from the sun. The flare produces strong waves of heat, light, X-rays, protons and electronics, which batter the earth for at least two days after the flare.

A scientist at the Sacramento Peak Observatory in California said that visually the flare was the biggest that observatory had seen in 25 years.

X-rays created by the sudden surge of heat from the flare produced almost instananeous effects on the earth. They first altered the density of the ionosphere, which serves as a reflector for short-wave radio waves.

The Federal Aviation Administration in Miami reported it lost radio contact with all airline flights moving north from Latin America. The Coast Guard said ship-to-shore traffic was lost from Boston to San Juan on the Atlantic Ocean side and around to New Orleans in the Gulf of Mexico.

"Comsat called us and said they were having trouble with satellite traffic and AT&T called with trouble on some of their long-distance radio linkups," the Solar Forecast Center's Heckman said. "Neither one explained to us what the specifics of their trouble were."

Solar activity has been on the rise since June 1976, when the sun reached what scientists call "solar minimum" in the 11-year sunspot cycle. The sun started flaring up this February, with as many as 200 small flares reported in the last three months. There have been three other major flares this year.