Continuing an upsurge that started last spring, serious crime in the District of Columbia jumped almost 33 percent in August over the same month a year ago, according to preliminary figures compiled by the D.C. Police Department.

The number of reported major crimes -- murder, rape, robbery, aggravated assault, burglary, larceny and auto theft -- now averages more than 200 per day, the highest daily average in almost a decade. This is still well below the all-time high in November 1969, when the daily average reached 265. The preceding year, Richard Nixon, campaigning for the presidency, had labeled Washington the "crime capital of the nation."

Police officials yesterday cited inflation, unemployment and increased availability of heroin and other illicit drugs as reasons for the current upsurge in crime.

Preliminary figures show that 6,451 major offenses were reported last month as compared to 4,860 in August 1979, an increase of 32.7 percent.

Murders more than doubled from 12 in August a year ago to 25 last month, the figures show. Robberies nearly doubled, from 530 in August 1979 to 1,000 last month. Burglaries increased by 626, from 1,089 in August a year ago to 1,715 last month.

Larcenies rose from 2,525 in August a year ago to 2,850 last month, according to the figures.

Auto thefts jumped from 300 in August a year ago to 510 last month, an increase of 210. Aggravated assaults increased by 20, from 285 in August 1979 to 305 last month. Rapes increased by 6, from 40 in August a year ago to 46 last month.

Major crimes reported per day last August averaged 209, according to the preliminary statistics. In July, the number exceeded 200 on several days, but the daily average for the month remained below 200.

Mayor Marion Barry and D.C. Police Chief Burtell M. Jefferson refused to comment on the figures.

During the summer, the mayor and the chief have wrestled with police department budget cutback proposals at the same time that many city residents were clamoring for more police protection.

A proposed layoff of 204 uniformed officers, however, was averted last week when the House Appropriations Committee voted to restrict the mayor's right to reduce the size of the police department. The committee said proposed cuts were unacceptable, "especially with the recent upsurge in the crime rate."