When independent trucker Donald Hamm left Rio Grande, Tex., Wednesday with a load of lettuce bound for Washington, he had heard horror stories of what might happen en route.

Driving days and stopping at night for safety, he reached the Farmer's Market on Florida Avenue yesterday, late but in one piece. "Coming through Houston they said a guy got shot at 15 minutes behind me," Hamm said. "You couldn't prove it by me."

Hamm, like a number of truckers, is working despite a week-long nationwide shutdown attempt by independent drivers and despite incidents of shooting and rock-tossing at trucks.

Food suppliers in Maryland, Virginia and the District said yesterday that independent truckers still running, such as Hamm, along with company and unionized truckers not affected by the strike, are keeping them well supplied, at least for now. They foresee shortages and price increases if the shutdown continues or expands.

Fresh fruit and produce are likely to be the most affected, according to suppliers, because independent truckers carry a heavy percentage of these perishables. Seafoods, meats and general merchandise usually are carried by trucking companies and unionized drivers, so those deliveries should not be deeply affected, they said.

The big food chains in the Washington area, Giant and Safeway, said they have experienced no disruption in produce deliveries. Spokesmen for both cited not a single missed delivery this week, though some trucks were delayed slightly.

Smaller operations are feeling the pinch more, mostly in price.

"The drivers are being intimidated," said Nathan Gordon, who owns Hampshire Produce Market in Takoma Park. The result has been a 10 percent increase in prices to him to offset the truckers' risks and the danger of tire-slashings and time spent laying over at night, he said.

Lonnie Kashif at the Farmer's Market said his costs rose 15 to 20 percent this week, with some products going "out of sight." He did not order cucumbers, he said, when he realized he'd have to charge 50 to 60 cents apiece for them.

An official of the Virginia Marine Products Commission said Thursday that truckers hauling seafood out of Hampton were shutting down, and that would idle some 4,000 Virginia watermen. A major seafood hauler in the Tidewater area called that report false and said there is "very little effect" of the strike on seafood deliveries because 80 to 90 percent of seafood in the Chesapeake area is hauled by private companies, not independents.

Independent truckers have stationed pickets outside the Dundalk Marine Terminal near Baltimore, the area's largest port, but officials there said operations were constricted only slightly. Harry Wills, assistant terminal manager, said truck traffic is down 25 to 50 percent.

Produce headquarters for the Washington area is the 38-acre Maryland Wholesale Produce Market in Jessup, where general manager George Maroulis said "things have been very quiet."

As for Hamm, he expects to be back on the road next week. The tax law that the independents are protesting "doesn't even start until 1984," he said. "The American Trucking Association is negotiating to get it changed. I may be just a dumb trucker, but common sense tells me that you don't shut down to protest something a year before it happens."