ALBANY, N.Y. (AP) _ When a New York State Thruway bridge collapsed without warning into a heap of steel and concrete, it also shattered confidence.

''It will create waves of public awareness throughout the country,'' said Gerard F. Fox, an engineer who also teaches bridge design at Columbia University. ''I think a disaster ... focuses people's minds on things. We always make great strides in bridge design from a collapse.''

The failure of the Schoharie Creek bridge on April 5, killing at least six people, shook public confidence in the bridges people use every day.

''This thing here is a special circumstance liable to make a guy look every time he goes over a bridge,'' said Ralph Burkins, owner of a shipping company whose 80,000-pound rigs rumble daily along the thruway.

The National Transportation Safety Board has begun an investigation of the disaster, only the fifth investigation of a bridge accident in the agency's 20-year history, said board spokesman Ted Lopatkiewicz.

The first followed the collapse of the Silver Bridge between Gallipolis, Ohio, and Point Pleasant, W.Va., into the Ohio River on Dec. 15, 1967, killing 46 people.

That disaster led to congressional hearings, a presidential commission, and finally a national standard requiring inspection of all public bridges at least once every two years.

The accident 35 miles west of Albany also may shape public policy governing bridges. This accident, like the 1983 collapse of the Mianus River bridge on Interstate 95 in Connecticut, struck a major regional arterial and involved loss of life.

It's also a significant accident because of the reputation of the New York State Thruway Authority.

''The Department of Transportation and the Thruway Authority in New York state are generally viewed around this country as of the highest level of competence,'' says Dwight Sangrey, dean of engineering and a specialist in risk assessment at Rensselaer Polytechnic Institute in Troy.

Sangrey says major bridge failures stem from disparate causes: structural deterioration, such as weakening of poorly maintained or aging supports; unforeseen events, like the freight ship that rammed the Sunshine Skyway near St. Petersburg, Fla., in May 1980; and acts of God, such as the rains that forced Schoharie Creek out of its banks.

What links the failures, says Sangrey, is a question: ''Is the inspection and maintenance of those bridges really up to snuff?''

It generally is, according to John Ahlskog, who runs the bridge inspection program of the Federal Highway Administration in Washington, D.C.

He said about 40 percent of the nation's 576,000 public bridges are considered either ''structurally'' or ''functionally'' deficient. They may require load restrictions or otherwise limited use. But Ahlskog says plainly dangerous bridges are closed quickly. ''The states are doing a pretty good job. The risk is minimal,'' he said.

A similar percentage of New York's 19,592 state and local bridges - 45 percent - is deemed deficient. DOT spokesman David Murray says only 393 of those are ''severely'' deficient.

The history of the 31-year-old Schoharie bridge demonstrates that neither inspections nor maintenance necessarily prevent accidents. The state extensively refurbished the 540-foot-long concrete and steel bridge, including replacement of concrete on support piers, in 1982.

State officials say the bridge passed inspection in April 1986. A further check of the structure's footings for erosion, also suspected in the collapse, showed nothing unsettling. State police even say the bridge was checked and looked sound the morning it crumbled into the river.

''I just don't understand it,'' said Daniel Garvey, chief Thruway Authority engineer. ''The bridge has not been without maintenance and care, but obviously there's something we missed.''

Gordon Batson, who teaches bridge design at Clarkson University in Potsdam, says even the most conscientious inspectors can be foiled by nature. He said surging flood waters from two straight days of rain could have flushed soil from beneath the bridge's underpinnings without any visible sign.

''If erosion of that riverbed takes place, it takes place very quickly,'' he said.

Batson said the inquiries into the Schoharie accident may eventually show a need for more underwater inspection. Indeed, Ahlskog said the federal government is already pushing the states that way.