A bulldozer driven by a vandal caused extensive damage early yesterday at the Northeast Elementary School construction site in Ellicott City, Howard County police reported.

Shortly before 4 a.m., county officers on a surveillance operation nearby heard what was described as a back-up beeper sound, then a loud bang from the school site in the 3100 block of Old Stockbridge Drive, said Denise Walk, a police spokeswoman.

Investigating the noises, the officers also heard squealing tires from a vehicle leaving Old Hollow Lane nearby, and found a trail leading there from the school site.

Walk said three construction trailers had been knocked over, and the bulldozer had been driven through the school.

A school system official estimated the damage to the school at $50,000, police said. No damage estimate for the trailers was available.