Three thousand more youngsters than originally planned will be given jobs under the District of Columbia's Summer Youth Employment Program this year at an additional cost of about $1.9 million, the D. C. Department of Employment Services announced yesterday.

Matthew Shannon, acting employment services director, said the added jobs will go to some of the 8,000 young people who had registered for the program but who did not get one of the original 17,000 jobs offered. Registration for the program is now closed.

"We had 25,000 youngsters registered," said Shannon, "and jobs for only 17,000. With such a large disparity in the numbers, we felt almost compelled to see if there was more money available for jobs, and the mayor asked us to devise a plan to identify the jobs and develop a plan . . . " to fill them.

Shannon said he did not know where the $1.9 million for the new jobs would come from, but he said about $1.6 million would go to pay salaries and the remaining $300,000 to pay administrative costs.

The city originally allocated $5.1 million for this summer's program, with an additional $7.4 million in federal funds provided under the Comprehensive Employment and Training Act CETA .

One-thousand of the added jobs will go to 14- and 15-year-olds, who will act as tutors for first- and second-graders in a program run by Associates for Renewal in Education and the public schools.

In addition, the Department of Housing and Community Development will employ 301 teen-agers in a program designed to rehabilitate deteriorating public housing units. The rest of the 3,000 will be placed at existing summer job sites, chiefly as general office assistants.

"Those young people who have not received notification that they have a summer job should keep their hopes up now," Shannon said. "We'll have the new notices of jobs in the mail by the week of June 14."

Before the added jobs were included in this year's program the number of summer jobs was the smallest in the four years of the Barry administration. When Barry ran for office in 1978, he promised to create 30,000 summer jobs but never reached that number.

In 1979, when Barry had a program with 28,000 jobs, criticism of the program was at its height with complaints from employers of too many or too few youngsters sent to work sites and complaints of foul-ups in them. Those criticisms continued in 1980 and Barry sent his key political advisor, Ivanhoe Donaldson, to take over as acting director of the employment services department.

Criticism of the program lessened last year as the number of youngsters employed dropped to 19,000, but employers still complained of problems in getting the number of young people they had requested for jobs.

This year, some of Barry's opponents in the race for the Democratic nomination for mayor have criticized the program for offering too many jobs in government and not enough with private employers.