The Transportation Department yesterday expanded its investigation into airline scheduling to include carriers flying into Denver, Newark, San Francisco and New York's La Guardia airport.

"The information obtained from our current investigations suggests that airline scheduling problems are widespread and that expansion of our investigation is warranted," Transportation Secretary Elizabeth Hanford Dole said.

The department had already been investigating American, Eastern, Continental, Delta, Piedmont, United and USAir, airlines operating out of Atlanta, Boston, Chicago's O'Hare and Dallas-Fort Worth airports.

Dole said the expanded investigation also will include Denver's Stapleton, Newark, LaGuardia and San Francisco international airports, locations where delays are mounting. The probe adds Aircal, Pacific Southwest and Pan American airlines to the list.

The probes are part of a renewed effort to address flight delay problems.

The government has asked for comment on a rule that would require airlines to disclose to the public on-time performance as well as other service-related information.

The government contends that some of the delay problems are caused by airlines scheduling too many flights during rush-hour periods.

Dole said that despite the delay problems, airline deregulation is working.

"Millions of Americans are in the air today visiting families and friends routinely or seeing parts of America they only dreamed about prior to 1978," Dole said.

"This has caused what was a stagnant airline market 10 short years ago to be one of the most dynamic markets in our economy today," she said.

"This expansion provides us with a tremendous challenge to stay ahead of the pace," she added.

Dole said about 70 percent of delays are caused by poor weather.

Earlier this year, the government granted major airlines antitrust immunity to hold scheduling talks that resulted in shifting about 1,000 flights at the nation's busiest airports to less-congested time periods