The number of poor children in District of Columbia public schools dropped by more than 14,000 from 1969 to 1975, according to a national survey released yesterday by the Department of Health Education and Welfare.

The reduction in the percentage of school children whose families live below the poverty level - from 23.2 to 15.7 per cent of total enrollment during the six years - could mean a loss of $3 million for the District if Congress reallocates federal funds for what it calls educationally disadvantaged children, an HEW official said.

Congress ordered the survey conducted jointly by HEW and the Census Bureau, to update 1970 census data for purposes of distributing $1.6 billion a year in so-called Title 1 monies of the 1965 Elementary and Secondary Education Act, which provides special programs for educationally disadvantaged children.

A spokeswoman for the D.C. public schools said she was unaware of the federally collected figures but said at least one city indicator appears to contradict the finding of reduced poverty here.

According to Mildred Cooper, assistant D.C. superintendent for research, the city's free and reduced lunch program has had a "pretty constant" enrollment over the last four years, and "those children wouldn't get the free lunch if they weren't poor."

The federal survey, which covered 151,000 households nationally, was presented as "reasonably accurate" although still preliminary.

The reported decline in poor children here was part of a more than 700,000-pupil drop-off throughout the South in those years, according to the survey. During the same period, both the number and proportion of children living in poverty increased in the northeastern, north central and western regions of the country.

Federal standards define poverty status as income of less than $5.500 a year for a nonfarm family of four.

Despite the decline, the 17 states of the South, from Texas to Delaware, still contained about 43 per cent of all U.S. school children living in poverty, or 3.1 million of the approximately 7.1 million poor children nationally, the survey found.

Of the remaining 4 million, about 18.6 per cent, or 1.3 million, live in the Northeast, 22 per cent, or 1.6 million, in the north central states, and 15.8 per cent, or 1.1 million, in the West.

The percentage of poor children among all pupils attending public schools in the Souit was also found to be higher than in other regions about 19.6 per cent. This compares with reported rates of 12 per cent in the Northeast, 11.6 per cent in the north central states and 12.9 per cent in the West.

Maryland and Virginia also had declining numbers of poor children during the six years, according to the report.

Maryland's enrollment dropped by about 13,000 poor children to 104,000 in the six years, while the state's poverty rate declined by less than 1 per cent, to 10.7 per cent.

Virginia lost a total of 59,000 poverty-level children, but the decline in the poverty rate was about 4.5 per cent, down to 13.7 per cent in 1975.

Based on the survey, Congress could shift up to $91 million in Title 1 money from the South, reallocating $37 million each to the Northeast and north central regions and $17 million to the West.

The District's current allocation of $10 million would be reduced to $7 million under such a formula and Virginia's $39 million would drop to $31 million. Maryland would lose none of its current $28 million.

Congress is scheduled to extend authorization of the funding this year and has prohibited HEW from altering the present distribution until new legislation is enacted, officals said.