Poor bridge maintenance by New York state officials led to riverbed soil erosion and the collapse of a highway span over the Schoharie Creek near Albany, N.Y., last year, the National Transportation Safety Board said.

The safety panel also warned that 43,000 bridges nationwide are overdue for inspection, and many may suffer from the same problems that caused the Schoharie span to collapse.Four passenger cars and a tractor-trailer fell into the surging flood waters on April 5, 1987, and 10 people were killed.

The board, which released a report Tuesday listing the accident's probable cause, issued an urgent recommendation to all states to inspect underwater bridge foundations as soon as possible for signs of soil erosion, or scouring, beneath the supports.

James Burnett, chairman of the safety board, said the probable cause of the bridge collapse was the failure of the New York State Thruway Administration to maintain the riprap around the base of the footing, which protects against scouring.

Riprap are huge, specially cut boulders piled against bridge piers to support over-water spans and prevent soil erosion beneath the bridge footing. A consultant hired by New York state officials in 1980 recommended replacing and adding boulders to the Schoharie bridge supports.

But a low-level state transportation official ignored the recommendation.

There was information that should have provided warning signs . . . but it wasn't acted on, said Dr. Bernard Loeb, deputy director of the board's bureau of accident investigation.

Mr. Burnett said the bridge probably would have survived had the boulders been replaced.

The board also blamed the collapse on ambiguous plans and specifications used for construction of the bridge. It said inadequate inspection by the Thruway Authority and lax oversight by the New York State Department of Transportation and the Federal Highway Administration, an arm of the U.S. Department of Transportation, also contributed to the accident.

The bridge was comprised of several sections, each built and supported separately without structural overlap. A continuous steel girder connecting

sections of the bridge could have prevented the individual segments from collapsing so suddenly and completely, board investigators said.

The Schoharie Creek bridge was built using design standards common from the 1940s to the 1960s, Mr. Burnett said. The span was supported by piers attached to large concrete blocks, called spread footings, buried in the riverbed. Large boulders were filed around the piers for added support and protection.

Swiftly moving river currents, however, can shift the boulders and allow water to wash away the soil beneath the footings. If the erosion is undetected by inspectors, the bridge may collapse.

The Federal Highway Administration requires that all bridges be inspected every two years, but Mr. Burnett said the agency admits at least 43,000 bridges nationwide are past due for an inspection.

He said federal officials do not know how many of these bridges are over water or how many may have been built using spread footings. But he said there may be thousands like Schoharie.

There are no federal standards requiring inspections below the water line for bridges that span rivers and creeks.

The board issued an urgent recommendation for states to conduct underwater inspections of all bridges located on shallow spread footings. The panel also told state and federal transportation officials to conduct in-depth studies to measure the stability of bridge supports.

The board urged the Transportation Department to withhold federal highways

funds from states that do not comply with national bridge inspection standards. DOT officials already have this right but board investigators said it has rarely been used.

Periodic investigations by the DOT inspector general to ensure the department is properly overseeing state bridge inspection programs also were suggested.

The board issued several recommendations to the American Association of State Highway Transportation Officials, including requests to update technical bridge inspection manuals to better account for the effects of scouring.