Mayor Marion Barry, who a week ago promised a summer job to every District youth between the ages of 14 and 18, raised the stakes yesterday by including those up through 21 in his blanket job offer.

"I'm guaranteeing everybody a job between 14 and 21, regardless of what your parents make," Barry said at his monthly press conference. "Double your money back if it doesn't work."

The youths must sign up for the summer jobs by Friday. In all, city officials expect about 22,000 young people to register for work -- about 2,000 more than were employed last year. Adding the 19-to-21-year-olds will cost an additional $800,000, bringing total city spending on summer jobs to $6.8 million.

The mayor also announced a new program to increase job opportunities for the city's Latino community, including the opening of a Latino Employment Services Center in Adams-Morgan and creation of a six-member unit within the D.C. Office of Personnel to monitor the city's hiring and training of Latinos.

The new program, which will cost an additional $200,000 this year, was authorized in the wake of complaints from Hispanic leaders that the administration has ignored the employment and social problems of the Hispanic community.

Some leaders also complained about Barry's treatment of Jose Gutierrez, formerly the highest-ranking Hispanic in the D.C. government, who was demoted recently after he publicly charged that the administration had sought to award contracts on the basis of politics.

"Developing these programs is a priority which grew out of my recent meetings with members of the Hispanic community," Barry said. "I have made a commitment to increase the number of Hispanic employes in the District government."

During an almost hour-long session with reporters, Barry also:

* Said he probably will sign legislation, which awaits final approval by the City Council next Tuesday, that would greatly ease controls on rental property in the city.

Barry said he objects to an amendment to exempt single-family homes from rent controls as they become vacant, but noted that the current rent control law will expire at midnight Tuesday and said he may have no choice but to sign the new law to maintain some level of controls.

* Hinted again that the District may award the Chesapeake and Potomac Telephone Co. the contract to install a telephone system in the new municipal office building at 14th and U streets NW, even though the phone company's system may not be the most economical and modern system available.

Gutierrez and others have alleged that the Barry administration has tried to steer the contract to C&P as a political favor to Delano Lewis, a top company official. Yesterday, Barry said that no decision has been made but that he doesn't want the city to do anything "that would vastly shrink the revenues of C&P" and force the company to further boost its rates for residential customers and cut back its work force.

* Defended his part in filing a multimillion-dollar lawsuit against George Nelson, a disabled laborer from Southeast Washington who was involved in a car accident in 1984 in which the mayor's wife, Effi, says she suffered severe neck and back injuries.

Barry said that Nelson was drunk when he rammed the rear of an unmarked police car in which Effi Barry was riding, and deserves to be punished criminally and civilly. Nelson's attorney has said Nelson pleaded guilty to a drunk driving charge stemming from the accident.

Mrs. Barry, who previously was treated for back problems, suffered a "20 percent disability" as a result of the accident and has difficulty moving her left arm, the mayor said, adding that his wife was the principal plaintiff in the suit -- in which the Barrys are seeking $2 million -- and that his name was added for technical reasons.

"My wife is operating on her civil rights as a private citizen to go after drunk drivers," Barry said. He added that "drunk drivers are dangerous, and I don't care what it the suit looks like."

The mayor boasted that his plan to offer seven weeks of summer employment to anybody between the ages of 14 and 21 is "revolutionary" and will help keep young people off the streets and out of trouble.

The city will first seek to place the applicants in private jobs. Failing that, the city will place the youths in jobs with nonprofit organizations, with the city paying the salaries; or in city government jobs.

The jobs will pay $3.35 an hour, and the city will offer drug treatment and counseling to those who request it. Officials estimate that 10 to 15 percent of the young people who sign up for jobs will not stay for the full seven weeks.

The District's new Latino employment center will operate at 2441 18th St. NW, with services coordinated by the Mayor's Office of Latino Affairs. The city also will offer a special summer job program for about 80 Latino youths.

In another development in Barry's touchy relations with the Hispanic community, the manager of a construction firm doing work for the city said two city officials went to job sites at the District Building and at police stations and demanded to see Hispanic employes' green cards.

William Johnson, the acting director of the D.C. Department of Administrative Services, acknowledged the incident. He said the two city officials had acted wrongly and that he will apologize to officials of G&C Construction, the firm in question.