Approximately 100,000 British truck drivers, about one in four, struck for more pay today. A dismayed and rattled Labor government said the action threatened national food supplies and could make another one million jobless in a week.

Headlined cries of "Chaos" and "Famine Threat" freightened shoppers and some stores soon reported shortages, from frozen food, salt and sugar to toilet paper.

Spokesmen for industry doubled the government's forecast, predicting that 2 million workers would soon be idle for lack of raw materials to process.

But hard facts on how much freight was moving and how much was immobilized were difficult to come by. The trucking industry here as in the United States is fragmented among thousands of concerns.

A spokesman for trucking fleets owned by 15,000 large corporations reported "patchy and spansmodic" interference with deliveries. These fleets, carrying nearly half the freight hauled by truck, are not on strike.

Whatever the actual state of affairs, the walkout by members of the Transport and General Workers' Union, Britain's biggest, is a serious blow to Prime Minister James Callaghan.

To fight inflation, he had hoped to limit pay increases to 5 percent. That prospect disappeared months ago and now the government wants gains to hold near their present level, 9 percent. But the truck drivers have rejected an offer of 13 percent -- they get $106 for a 40-hour week -- and so the pay-price spiral would mount.

On the political front, the strike undermines the Labor Party government's claim that it gets on best with unions. Margaret Thatcher, the Conservative leader who hopes to become Britain's first woman prime minister before the year is out, has sensed that the public mood is hardening.

Almost every day, she hits out at Callaghan for his alleged ineffectiveness and proposes new measures to curb union power.

Whether the truck strike seriously disrupts daily life here largely depends on the union's picketing tactics. Even before the strike was declared, rank and file drivers, clearly pushing their less militant leaders, picketed ports and blocked supplies going in and out of this island.

The union's chief, Moss Evans, has said his men will picket only employers against whom they are striking, the large trucking companies. But it is not clear that Evans can control the drivers.

On paper at least, the strikers haul less than one ton in three of all freight in Britain. Nonstriking drivers work not only for large corporations' fleets but also for a government company and for themselves.

Britain is heavily dependent on trucks. Tains, barges, ships and planes only carry one ton in eight. But if pickets do not interfere, the nonstrikers could keep food, raw material and finished goods rolling.

Today, supermarkets reported a mixed picture. The Safeway chain, for example, said its stores in southern England were well supplied, those in the Midlands were badly hurt by pickets at a central depot and stores in Scotland were partly supplied.

Elsewhere across the country, strikes were looming, in progress and settling:

Oil tanker drivers have ended their threatened stoppage with a 15 percent deal. But those in Ulster refused to sign. The government declared an emergency there and moved in 600 extra troops to deliver gasoline and fuel oil.

British Airways got only 18 of 500 flights into the air today. Pilots struck for 24 hours, angry because the wrong crew had flown a London-Paris run.

There was a break in the five-week-old strike of provincial journalists. Those at the Portsmouth News agreed on a 14.5 percent increase and the rest of the 9,000 strikers are expected to follow their lead.

The country is likely to go without trains on two days next week. The locomotive engineers plan brief strikes to press their claim for more now, three months before their contract expires.

Around Manchester, 1 million citizens were warned to boil all drinking water. About 400 sewer and water workers have struck and untreated sewage is polluting rivers and streams.