Cracked runways, the latest problem for Denver's long-delayed new airport, will raise maintenance costs for the runways' entire 40-year life span unless they are dug up and fixed right, according to an expert consulted by The Associated Press.

City officials say the thousands of cracks and holes are being repaired and will not recur.But Fu Hua Chen, one of the world's leading experts on expansive soils, said the fissures are "a good indication that in the future, we'll have serious problems with these runways" unless they are torn up and the earth beneath them replaced.

The $3.7 billion Denver International Airport was built 23 miles northeast of the city after officials decided that Stapleton International Airport could not be expanded to accommodate increased air traffic.

The airport was supposed to open in October 1993. That date was pushed back four times by construction delays and, most recently, problems with the new high-tech baggage system, which had a tendency to lose or chew up bags.

Mayor Wellington Webb has said the airport will use conveyor belts and carts for luggage until the new system can be fixed. He has refused to say exactly when it will open.

The airport is built on one of the country's worst areas for soils, which expand when wet and crack even the strongest concrete.

Before the runways were laid, the top six feet of soil were scraped away and the area was leveled. Then the soil was replaced and the top 12 inches mixed with lime to reduce expansion.

Since the cracks appeared - some 10 to 20 feet long - workers have ground down thousands of square yards of uneven concrete and patched fissures with glue.

More than seven gallons of epoxy were injected into one monster hole on one of the runway aprons, said Graham Barber, supervisor for the contractor Bangert Bros. The company is making the repairs under a one-year warranty that took effect when the city accepted the runways several months ago.

Peter Stokowski, DIA's senior engineer for runways, said he did not know how much contractors have paid for repairs or how much continuing repairs would cost. Chen did not estimate how much continuing repairs would cost.

The Federal Aviation Administration, which must certify the runways, does not allow runway slabs to be ground down more than half an inch. That could cause further trouble if the slabs continue to heave.

Chen, who toured the airport at the request of the AP, said the grading and gluing would be inadequate in the long run. He said airport managers should shut down individual runways while each is repaired properly.

Stokowski said the problems have been fixed to the satisfaction of the city and the FAA.

He said the problems have included drooping runway edges, missing or improperly inserted dowel rods connecting runway sections, lumps of clay in concrete and holes inside the runway caused by large air spaces.

Trucks also left potholes when they drove on the runways before the concrete was fully cured, he said.

"However, these are normal types of construction problems that occur," Stokowski said.

Stokowski said he could not estimate the number of cracks and holes that have been patched or filled. Other engineers and an AP reporter who toured the runways with Chen estimated that there were thousands of repaired spots.

Stokowski said the cracking and buckling was caused by poor alignment of the concrete pouring machines. Although the city had access to more expensive laser-guided machines, the contracts did not require their use, he said.

Much of the problem also was caused by concrete shrinking, which left surface cracks that were easily repaired, Stokowski said.