For the third time in as many pay periods, D.C. Mayor Marion Barry's summer jobs program for youths failed last week to pay thousands of teen-agers on time.

As a result, hundreds of angry youths clamoring for their paychecks besieged the jobs programs headquarters for the third time. City officials scrambled to write checks to pay about half of the 3,000 unpaid youths Tuesday, and paid another 600 after retrieving checks that had been sent to wrong locations.

The youths were to have been paid last Thursday and Friday, but as of yesterday about 900 of the 22,000 in the program still had not gotten their checks for the last two-week period, city officials said. The officials said a number of youths may not have been paid at all this summer.

"I would bet my bottom dollar that there are some (unknown, unpaid youths) out there. We'll find out when they start screaming," said program spokesman Adolph Slaughter.

City officials have blamed the failure to deliver the checks on time on the ineptitude of many of the 2,400 worksite supervisors, understaffing at the jobs programs offices throughout the city, youths who don't show up at the right place and time for their checks and on a computer breakdown last week.

But many of the teenagers, along with their parents and job supervisors, say they are confused and outraged with the "system" that gives different answers every two weeks at pay time, but results in the continuing problems.

This is the second summer that Barry's summer job program has been plagued with payroll problems, despite the reorganization of the administrative staff and the hiring of an additional 200 staff workers.

James Brown, 14, said he takes three buses from his home at 5549 B St. SE to his worksite in the Brentwood section of Northeast Washington. sHe and 65 other teen-agers sweep streets and alleys for four hours a day and are paid the minimum wage of $3.10 an hour.

But 20 of the 66 youths, including Brown, said they have not been paid all summer.

His mother, Hattie Brown, got angry after program officials informed the kids that they "didn't exist" after they had been working one month. The next day, a regional supervisor promised the checks would be ready the following day, she said.

"The kids came in on that Friday and found no checks," said Brown. [The worksite supervisor] went down to 222 C St. NW (the program headquarters) and got the biggest runaround of life.She got so mad she left. They have told her she'd be getting the (checks) every week since, and there have been no checks yet."

Mrs. Brown said the supervisor went to a regional jobs program office at McKinley High School Tuesday and was told that the checks had been sent to the wrong office and now will be delivered tomorrow.

Mrs. Brown has organized a sitdown strike by the 66 youths to last until Friday, saying it is the only constructive alternative to thr youths walking off their jobs.

Last Thursday and Friday the central computer for the jobs program spewed out more than 17,000 checks, but many of them were delivered to the wrong worksites and had to be returned to the program headquarters for resorting. One batch intended for the Metropolitan Boys and Girls Club ended up at the personnel office of the Metropolitan Police Department.

Rick Sowell, director of the Crispus Attucks Park of the Arts, received 387 checks for his workers, but 147 of them belonged to workers elsewhere. tr for add 5

"The system stinks," said Sowell, on his way to try and calm 50 to 60 youths who mobbed the jobs headquarters Friday after reports that one of the policemen guarding the building had pulled a gun.

Long an outspoken critic of the program, Sowell and other representatives of community groups said they have offered advice and manpower to expedite and improve the system but that program officials have refused their offer.

One site director with more than 20 years' experience in city programs blamed this year's problem on the city's attempt to correct last year's errors by bringing in a host of new and inexperienced staff people.

"The checks have always been a problem, but at least last year, you always knew whether they had a check or not and if a check was lost, you could track it down," the site director said. "This year you can't do that."

Kemry Hughes, 18, the head of the Mayor's Youth Leadership Council, was among the teen-agers seeking answers to the check problem last Friday. He hasn't been paid this summer either.

"I haven't found out anything yet, I'd like to get an explanation from (William R.) Ford (director of the D.C. Department of Employment Services) of the mayor," he said.

But Larry Wilson, 20, of Southeast Washington, was typical of the more desperate youths who have counted on the checks they have not received.

"I've been coming down here three Fridays running. I've borrowed so much money just to get to work, that when I get my check it won't even be mine," he complained to the crowd.