Two weeks ago, Frederick (Buddy) Wilkerson said he sent work crews into neighborhoods throughout the Washington area to replace hundreds of azaleas, boxwoods, hollies and other ornamental shrubs killed or wounded by the severe cold of the last two winters.

"We try to explain to people that they should not dig up a plant just because it may still be brown," said Wilkerson, manager of the 250-acre A. Gude Sons nursery in Rockville. "We suggest that the people just water, fertilize and wait."

Wilkerson, whose nursery plants suffered serious damage, is among thousands of area residents trying to salvage their favorite greenery from the ravages of the last two winters.

Dr. Francis R. Gouin, associate professor of horticulture at the University of Maryland said the winter of 1976-77 the coldest in 40 years in the continental United States, seriously weakened many plants that then were given the final death blow last winter.

"It was not just a problem of cold temperatures," Gouin said. "But there was also damage to plants from wind, sun and frozen ground. There was one period when the ground was frozen three weeks. This meant that water could not move up into the stems of the plants, and they died."

Gouin said most of the winter damage was incurred by broad-leafed evergreens such as azaleas, camellias and hollies, with substantial damage to dogwood blossoms and jasmine blooms, which were greatly reduced this year.

According to a spokesman for the National Park Service, the White House will spend $10,000 this spring to replace hundreds of azaleas, hollies, some small cherry trees and huge patches of ground ivy killed last winter. The previous year, $25,000 was spent to replace White House shrubs killed during the winter.

In the mall area near the Lincoln Memorial, the Washington Monument and around the Tidal Basin, large numbers of cherry trees, elms, and maples - some of which were between 25 and 50 years old - were killed by severe weather, according to a Park Service spokesman, who said the replacement cost is about $200,000.

National Weather Service figures show that in the calendar year of 1977, temperatures dropped to 32 degrees or below on 75 days. In 1976, that level or below was reached on 77 days.

Gardening expert Tom Stevenson, whose column appears in The Washington Post and 450 other newspapers throughout the United States, believes that the sustained cold periods provide the key to wide-spread damage incurred by ornamental plants.

"Last winter (1976-77), the ground was frozen for a longer period of time and freeze was much deeper than this winter (1977-78)," Stevenson said.

"A lot of plants never had a chance to recover from the effects of the previous winter before they were hit with another tough winter this year," he said.

In addition, Stevenson said that not all of the brown-leaved plants are victims of winter cold. He said problems such as insects, disease and generally poor care also could have a similar blighting effect.

To revive plants that may still be brown but show signs of some live tissue, Stevenson recommends that the plant immediately be given a hefty dose of fertilizer.

Gouin suggested that absolutely no fertilizer be given a sickly plant until it shows definite signs of new growth. He said a concentration of fertilizer on weak plants can burn roots seriously.

When replacing winter-damaged plants, Gouin said that homeowners should consult experts to learn which plants are considered to be hardy in the Washington area.

To replace winter blighted azaleas, for example, he suggested a replacement with the Gable Hybrid azalea, a plant that produces fewer blossoms than many others but thrives in the more frigid northern states.

Dr. John L. Creech, director of the National Arboretum at 24th and R streets NE. said a major problem in this area is that many shrubs and trees that grrow without difficulty in the southeast United States are transplanted here to whats considered the "border line" between northern and southern growing regions.

"We bring broad-leaved evergreens like magnolias into northern areas to grow, and sometimes they fail," Creech said.

Among the Arboretum's many thousands of plants, Creech said that the collection of about 1,100 camellias - which grow well in the warmer temperatures of the Deep South - suffered the worst winter damage.

Creech said 123 camellias and 70 other large plants in the camellia area, including Burford holly and Chinese holly, died due to the severe winters.

Creech said replacement of the camellias at an approximate cost of $200,000 will provide an opportunity to install more advanced varieties of the plant which, hesaid, might withstand the ravages of winter.