Mayor Marion Barry promised a summer job yesterday to every 14-to-18-year-old in the District who wants one, saying that would help keep the city's youth away from drugs.

In the past, the city's summer youth jobs program has been limited by the amount of money available.

City officials originally estimated they could finance 17,000 summer jobs this year, but Barry said yesterday the city now expects to register and employ 25,000 teen-agers. To be eligible, teen-agers must register with the city by April 26.

"I am personally guaranteeing a job for every young person between the ages of 14 and 18 who registers for our program," Barry said yesterday at a news conference at Dunbar High School. "This is unprecedented. I know of no other mayor who has ever undertaken such a challenge."

He asserted that while the District is No. 15 in population, it is No. 2 in funding summer youth jobs.

The city's summer jobs program, which uses both federal and city money, financed 20,110 jobs last year, a spokeswoman for the D.C. Department of Employment Services said.

The city budgeted $6 million for this summer's youth jobs, and Barry said he will ask the D.C. City Council to add another $800,000 to $900,000 for the expanded program. The city also expects to get $5.7 million in federal funds.

"I'm appalled and saddened by reports that some of you have not been able to work for the summer," he told a group of Dunbar students. "But also I'm concerned about another aspect of our society and that is the increasing drug use in our schools and our neighborhoods and communities."

Early in his administration, Barry embarked on a huge youth summer job program for about 30,000, but it turned into a disaster.

Thousands could not start work on time because of delays in processing their papers; teen-agers were sent to the wrong work sites, and they had problems getting their paychecks.

"I couldn't have made this commitment [to guarantee jobs for everyone] in 1979 or 1980 . . . but now we know how to do it," Barry said.

So far, the District has identified 19,271 jobs, 41 percent of them with government agencies and the rest with nonprofit organizations.

The city is also sending letters to 11,000 local private employers asking them to hire youths, and Barry said that he would start taking summer youth hiring into account in deciding whether the city should support requests for help from local businesses.

"We keep our own data and statistics. A number of business people come to the city for various kinds of support for their projects, and we think it ought to be reciprocal," Barry said. "You want your projects supported, you support our project."

"If all else fails, the city government will still pay for the hiring of these young people," he said.

"Either we invest the money in the front end or we invest it in the back end in terms of paying to keep people in D.C. Jail or Lorton or Cedar Knoll or Oak Hill," the mayor said, referring to the city's youth and adult penal institutions.

The seven-week job program runs from July 1 to Aug. 16. Registration is open to any District youth or girl aged 14 to 21.

Participants earn at least the federal minimum wage of $3.35 an hour and work a minimum of 20 hours a week.

Jobs include library assistants, child-care aides, laboratory assistants, groundskeepers, lifeguards and carpenters helpers, among others. While the federally funded portion of the program is limited to low-income youths, the District's program has no income limit.

"Young people should not be punished because their parents work. It seems to me that's idiotic, it ought to be reversed," Barry said.