Serious crime in the District of Columbia jumped an estimated 4 to 5 percent in the third quarter this year over the same period last year with larcenies and burglaries from office buildings accounting for most of the increase, Police Chief Burtell Jefferson said yesterday.

The increase follows decreases recorded in the first two quarters this year.

Specific figures for the third quarter will not be available for several days. But Jefferson took the occasion of department promotion ceremony yesterday to warn police officials of the preliminary findings and urge them to take additional steps to curb what could become an upward trend.

In an interview after the ceremony, Jefferson blamed the upsurge on increased unemployment, especially among youths in the city, and on a hard criminal core of criminal repeaters released on bail, parole or probation.

Federal statistics show overall unemployment in the city substantially lower this summer compared to last summer. Unemployment among black teenagers, however, increased from 32.9 per cent in August this year, according to official statistics.

Jefferson said that at a recent meeting of police chiefs from around the county, many big city chiefs told him they, too, were experiencing increases in criminal activity.

Crime analysts in the D.C. Police Department said they still lack final figures, but much of the increase appears to have occurred in the second district, especially its burgeoning commercial areas downtown, and Friendship Heights in Upper North west near the Maryland line.

In addition to market increases it reported larcenies, burglaries and robberies, the city was hit by two double murders and one triple murder during september, bringing total homicides for the month to 28, six more than the number reported in September 1977.

Jefferson said a sptcial nine-man task force of detectives has been assigned to concentrate on the multiple murders.

Among the 29 police officials promoted at yesterday's ceremonies was Insp. Lloyd W. Smith, promoted to deputy chief and put in command of the second district. Smith succeeds Deputy Chief George L. Chapoutot, who retired.

Two Captains, Howard B. Long and Clay W. Goldston, were promoted in inspector rank.

The large number of promotions resulted in part from the retirement at the end of September of 50 officers and officials who had to retire before the first pay period in October in order to apply the recent federally mandated 5.5 percent cost-of-living pay increase to their retirement pay.

The D.C. Fire Department also has lost several officials to retirement recently, including three deputy chiefs. They are Joseph R. Jeffrey, the fire marshal, replaced by Carmel Del Balzo; John P. Breen, director of training, replaced by Leonard R. Hanback, and James H. Lambert, a platoon leader in the fire fighting division, replaced by Dennis N. Logan.