It was a little over a year ago when a Texas businessman named Tommy Grant flew from Houston to Washington to deliver a warning: the steel bolts that hold together the nation's airliners, buildings, bridges and military hardware may be dangerously weak.

The reason, Grant explained to anyone who would listen, is that the bolts are counterfeits -- as phony as the ''Gucci'' handbags peddled by sidewalk vendors at ridiculously low prices.

The bogus bolts are made of cheaper steel alloys, and the counterfeiters cut corners in the hardening process, but they stamp their products with forged industry markings that give them the outward appearance of the real thing. Like the fake Guccis, the substandard bolts are snapped up by bargain-hunting buyers unconcerned with shoddy material and workmanship.

Grant is a whistleblower with a healthy self-interest to motivate him. He manufactures genuine steel bolts, and like other honest producers, he's being undercut by the low prices the counterfeiters can offer for their substandard fasteners.

And of course the potential for disaster in these literal weak links is far greater than the disappointment over a handbag that falls apart in a few days. When counterfeit bolts turn to putty or stretch out of shape at high temperatures or under other conditions of stress, it could cost the lives of those using the planes, tanks or bridges involved.

Despite the seriousness of his mission, Grant found it difficult at first to have his warnings taken seriously. The Pentagon brushed him aside, as it has other bolt experts. Nuclear Regulatory Commission officials were skeptical of Grant's charge that crucial equipment in nuclear power plants was assembled using steel bolts that wouldn't hold up in an emergency.

Grant finally found a receptive ear in Rep. John Dingell (D-Mich.), chairman of the House Oversight and Investigation Subcommittee. Dingell plans hearings on the bolt problem this month. We also launched an investigation after Grant dropped by our office one day. The evidence gathered by our associate Stewart Harris was alarming indeed:

Engineers for the state of Florida concluded that the creaking noise coming from a drawbridge in West Palm Beach was caused by counterfeit bolts stretching out of shape every time the bridge was raised for a passing ship.

Some 4,000 bogus bolts had to be replaced in the steel framework of a municipal garage being built in Beachwood, Ohio.

NRC inspection reports indicate that substandard bolts may have been used in about a dozen nuclear power plants. But government inspectors have rarely followed through with appropriate testing. Officials at one plant identified counterfeits in their stockpiles.

One out of every five purported Grade 8 steel bolts tested at the Defense Industrial Supply Command in Philadelphia turned out to be counterfeit. Grade 8 bolts are the workhorse of the transportation and defense industries; hundreds of them are used in every car, truck and tank that rolls off the assembly line.

Particularly shocking was the evidence that came in from manufacturers of military vehicles. They bought their bolts from distributors, relying on assurances that the bolts were properly made of high-quality steel. What they learned was that some distributors had been ordering substandard bolts from foreign manufacturers who stamped them to look authentic.

BMY, which builds M109 self-propelled howitzers, tested 750,000 supposedly Grade 8 bolts in its inventory and found that 250,000 didn't meet the standards. FMC, maker of Bradley Fighting Vehicles and M331 personnel carriers, told us that 20 to 30 percent of its bolts fell short of Grade 8 standard specifications. Army documents showed that one-half of the bolts stockpiled by Emerson Electric, another major defense contractor, were counterfeits. Two additional defense contractors reported counterfeits in their warehouses.

Last November, the Army granted waivers to the five defense contractors so they could continue using substandard bolts until Feb. 1, 1987. After that, all the companies had to purge their stockpiles of the bogus bolts. That decision made Tommy Grant hopping mad.

Grant says he'll explain to Dingell's subcommittee the twofold threat that stems from the waivers: In addition to the possibility that weak bolts continued to go into the vehicles, the waiver could jeopardize possible prosecutions being prepared by Defense Department investigators. Bolt suppliers will be able to point out in court that their counterfeits must be adequate to do the job -- because the Army permitted the companies to continue using them from November to February.