Washington's white population, which fell dramatically for more than three decades after World War II, appears to be increasing in the 1980s, according to a survey released yesterday by the Greater Washington Research Center.

The survey, conducted by telephone last year, indicates a major upsurge in the number of Hispanics and a continued decrease in the number of blacks, which began around 1970.

As a result of these shifts, the center said, blacks made up 65.6 percent of District residents in mid-1986, down from 70.3 percent reported in the 1980 census. The proportion of whites rose from 26.9 percent to 29.6 percent, while the share comprising people of other races, chiefly Hispanics and Asians, increased from 2.8 percent to 4.8 percent.

George and Eunice Grier, the demographers who conducted the 6,500-household survey for the research center, estimated that the District's total population last year was 629,200 -- down 1.4 percent from the 1980 census count of 638,333, but slightly above the Census Bureau's 1986 estimate for the District of 626,000.

The proportion of blacks in the District's population reached its peak -- 71.9 percent -- in estimates prepared by the Census Bureau for 1975. The bureau has issued no figures by race for cities or states since 1980, but it is expected to release estimates for 1985 this fall.

Although the research center report shows a continuation of trends that appeared in the 1980 census, David Word, a bureau demographer who is preparing the racial estimates, said that the changes "look too sharp." Word said, "It's hard to believe that the 1990 census count will show that type of population shift. It would be the first time in U.S. history that a major city became considerably less black than it was in the near past."

D.C. government estimates for 1985 show a small increase in the number of whites and a small decrease in the black population, but each is much less than what the Griers report.

"We're convinced our figures are right," George Grier said. "A lot of the whites moving in are young singles and childless couples. They don't have kids. They don't die. It's hard for the city or the Census Bureau to find them."

He said population estimates for wards indicate that the bulk of the white increase has occurred in Ward 3, the area west of Rock Creek Park, which was 91 percent white in 1980 and contained almost half the city's white residents.

The greatest declines in the black population, Grier said, appear to have taken place in wards 7 and 8, east of the Anacostia River. These two wards were among the city's poorest in 1980 and had the highest proportion of blacks.

Dennis E. Gale, director of the Center for Washington Area Studies at George Washington University, said housing renovation in neighborhoods close to downtown, such as Capitol Hill, Dupont Circle and Shaw, may account for some of the white population increase. But he said it appears that this "gentrification" has been moving at a slower pace recently.

The new survey and subsequent analysis were financed by a $230,000 grant from the Rockefeller Foundation and $90,000 from the District government.

Over the next few months, the Griers plan to release data on suburban Washington.

In 1974 the Griers directed a similar mid-decade census update, which foreshadowed many trends that were confirmed by the 1980 census.

According to the new data, the District's white population grew between 1980 and 1986 by 14,300, or about 8 percent to 186,100, while the number of blacks decreased by 36,300, or about 8 percent to 412,600.

The number of Hispanics reached 34,200, about 5.5 percent of the District's population and double the count reported by the 1980 census. Under the Census Bureau definition, which the Griers followed, Hispanic is an ethnic designation that includes some whites, blacks and people of other races. Previous immigration and school attendance data have indicated that most of the Hispanic newcomers here are from Central America.

Last week the Census Bureau reported that the number of Hispanics in the United States has risen 30 percent since 1980.

Overall, the report said, the city has had a substantial increase in the number of people aged 20 to 44, particularly in the 35-to-44-year-old group, which now includes many of the post-World War II "baby boom" generation. This was offset by a decrease in the number of children, particularly among blacks, and in the 45-to-64 age group of both races.

The population over age 65 was virtually unchanged, with a decrease in the number of elderly whites offset by an increase in blacks.

The census each 10 years is conducted by mail, with door-to-door follow-up as necessary.

Fred L. Greene, the D.C. government's planning director, said that he had not studied the center's new figures but said that he "really would question the reliability of a telephone survey," such as the one the center conducted. Greene noted that many more black households than white ones in the District lack telephones -- 6.3 percent compared with 1.9 percent in the 1980 census -- because of low income.

Grier said the survey figures were adjusted to account for phoneless households. He said random digit dialing techniques were used in the sample to include those with unlisted telephones.

Overall, he reported, the number of households in the District rose to 257,300 in mid-1986, an increase of 4,200 since 1980. This compares with a decline of 9,400 households in the District during the 1970s. The figure for total population includes an estimate of people living in institutions, college dorms, barracks and other types of group quarters, based on the 1980 census.