The digital thermometer at a nearby bank read 100 degrees yesterday as Carmen and Larry Miller trudged along Barton Street carrying three plastic gallon jugs of water for their downtown Arlington garden.

It was a stingy watering for their 600-square-foot plot planted with tomatoes, cucumbers, corn, lettuce, marigolds, zinnias, snapdragons, petunias and bee balm, to name just a few. It also was the legal limit under Arlington's water restrictions imposed after a water main break last week.

Yesterday's scattered thunderstorms that left a quarter inch of rain in the metropolitan area made little impact on the record drought that has made it a rough year for the Millers and the other 30 or so inside-the-Beltway farmers at 10 Barton Gardens, a community plot near the county courthouse. But most are taking the latest setback in stride.

"How can you be mad?" asked Carmen Miller, a community gardener for five years. "You deal with what is. It's like the farmers. You get a good year and a bad year."

The troubles of Washington's back yard gardeners echo, in miniature, the more serious plight of farmers without enough water for their crops. Spider mites, mealy bugs and other pests are prospering, and some pesticides will not work against them unless activated by water. The dryness takes a heavy toll on shallow-rooted plants such as annuals and some shrubs such as azaleas and rhododendrons. Tomatoes are falling victim to "blossom end rot," in which tissue collapses.

"If I had to put it on a scale of one to 10, I would say it's about on the order of nine, with 10 being the worst," said Larry Shapira, who teaches horticulture at Northern Virginia Community College during the week and dispenses plant lore at Merrifield Gardens on weekends.

His advice is to mulch lightly around plants to conserve moisture, to soak twice a week rather than water lightly every day, and to concentrate on costly trees and shrubs rather than trying to keep the grass green.

Shapira said there is nothing to prevent gardeners from planting anything in 1986 that they would plant in a damper year, except maybe grass, as long as they know how much water to use and are not under restrictions. "Most people are coping pretty well," he said.

One such success story is Harry Eghiazarian, whose lawn in North Arlington is Technicolor green and whose garden is lush. He pinched off a basil leaf from a sprightly plant and pointed to reddening tomatoes, crisp cucumbers and an adolescent eggplant. He is not worried about the new water restrictions.

"Nature will take care of it from here on," said Eghiazarian, who describes himself as "over 65."

Dorothy Michaels was not so lucky. Her Arlington back yard is full of grapes, berries and tomatoes, but the rest of the crop has dried up. "There was supposed to be lettuce here," she said, pointing to a bare patch of ground. She moved her finger over a few inches and squinted. "That was supposed to have been beets. Maybe there will be one."

On the other hand, Michaels acknowledged, "I haven't really watered it that much more this year, not like I should have."

It is not just the current crop at stake. Manny Terminella, another Barton Street gardener, said he is weighing whether it is worthwhile to put in fall crops -- spinach, onions, beans or other plants that will yield through the end of October. Maria Chau had been planning to transplant tomatoes and bell peppers, but she now is not sure.

The drought has not stunted everything at Barton Gardens, said Carmen Miller as she yanked a green stalk from the ground. "The weeds do very well," she said, "whether you have a drought or not."