After failing three straight times to pay thousands of summer youth workers on time, if at all, District of Columbia officials are counting on a new distribution system, and a little help from the U.S. Postal Service to make tomorrow's payroll tomorrow.

Program director Rudolph Van Slaughter said yesterday that 3,500 checks were mailed to workers' homes yesterday and 2,500 will be sent out today. Another 9,500 checks have been delivered to the 33 largest employers in the program, where the bulk of the youths work, for direct distribution to the youths.

Responsibility for the program's 2,800 scattered work sites, each formerly considered as a separate employer for pay purposes, has been consolidated into 614 employers, includig the 33 largest representing two-thirds of the sites.

By allowing the biggest employers, including the Peoples Drug Store chain, the D. C. Department of Recreation and the D.C. National Guard, to handle their own checks, program officials hope to free more than 100 of their staff workers to concentrate on getting checks to the large number of smaler firm employers, who previously were neglected.

"Instead of 175 people trying o cover 2,800 sites we now have 125 to 150 covering 581 sites," said Von Slaughter.

Von Slaughter said that many of the problems with the discarded pay system "can be laid to original poor planning."

He said that under the old system staff workers known as Youth Program Monitors (YPMs) had to make at least two trips to each work site to distribute blank time cards, pick up completed ones and distribute checks. If for any reason a youth was not present when the YPM delivered the check, it had to be returned to headquarters.

Von Slaughter said there were not enough YPMs to keep up with the large number of work sites, and that many of the YPMs quit out of dissatisfaction with their jobs, returned to college or have been fired.

Van Slaughter declined to comment on why consolidation of responsibility for the 2,800 sites had not been tried earlier.

Program officials admit that an unknown number of youths still will be missing checks when the program, recently extended one week, ends next Wednesday. In addition to continuing use of their swamped "complaint line," 727-9782 through 727-9786, beginning next week the officials will operate an office where the youths' pay problems can be dealt with on a face-to-face basis. Von Slaughter said the entire pay check difficulty would not be settled before October.