A line of violent thunderstorms packing torrential rain squalls and wind gusts of up to 68 miles an hour, brought brief respite yesterday afternoon from the grip of record-breaking heat plaguing the area.

The storms hit as the temperature reached a high for the day of 98 degrees, tying a record set in 1933 and prolonging the bake-oven atmosphere of an area that had just recorded July as the hottest month ever since the weather service began keeping records.

High winds uprooted hundreds of trees and interrupted electrical power service to more than 56,000 area customers. By late last night, power to all but about 2,200 customers had been restored.

At least two persons were injured seriously enough to be hospitalized. They were two house painters working in Arlington who were burned when the metal ladder on which they were working was blown onto an electrical power line by one of the cluster of storms that hit in the 500 block of N. Piedmont Street.

Paul Sims, 33, was reported in satisfactory condition at the Washington Hospital Center, where he was being treated for burns over 20 percent of his body. His brother, David W. Sims, 35, was listed in stable but guarded condition in the surgical intensive care unit of Arlington Hospital with burns on his arms and legs. No information was available on the addresses of the two men.

The same kind of gust peeled a metal roof from a cargo warehouse at Dulles Airport, where peak swirl measured in the area was clocked at 68 miles an hour.

But despite the damage done by the storm, it drove down temperatures from the blazing 98 level to 83 degrees within a couple of hours. The relief that brought, however, was tempered by weather service assurances that the heat was merely drawing a deep breath, and would hover over, around and about the area for the indefinite period.

While the storms brought welcome but short-lived cooler temperatures to the Washington area, meteorologists warned that the end to the month-long heat wave still was nowhere in sight.

Temperatures today are expected to rech 95 degrees, and Sunday is forecast to be another 98-degree scorcher.High temperatures also are expected for at least the first half of next week.

Yesterday started off destined to be a scorcher, with an early-morning temperature of 85 degrees recorded at National Airport. And all day long, the temperature and the humidity raced one another toward the 100 mark.

From Shaw to Chevy Chase, from downtown to Anacostia, Washingtonians spent most of the morning and early afternoon sitting on their front stoops, sprawled across park benches, congregating in air-conditioned office buildings and repeating the oldest and most over-used "How hot is it . . . ?" jokes.

The storms dumped little rain, and passed through the District largely unnoticed. But Virginia and Maryland were harder hit, mostly by high winds.

The Virginia Electric and Power Co. reported 36,750 homes without service shortly before 3 p.m. Repair crews were on the streets an hour later. sThe Potomac Electric Power Co. reported 20,000 homes without power in the storm's wake, mostly in Montgomery County and Prince George's County, with some scattered power outages in Northwest Washington.

News that the heat wave will continue came as one of Vepco's nuclear power units was shut down unexpectedly because of a leak in a steam generator.

Loss of the 775-megawatt Surry 1 unit in the middle of this power-sapping heat wave means that Vepco customers will have to pay more while the company switches to buying electricity or using costly fossil-fired plants.