Would you hire William Castro, a 28-year-old methadone user who has never held a steady job? What are the odds that Michael Johnson, 18, who worked on cars a little bit before being sent to prison for armed robbery can find a job?

The odds are better than hopeless despite this city's 16 per cent unemployment rate because Johnson and Castro are participants in a supported work program.

Supported work programs are aimed at the hard-core unemployables - ex-prisoners, ex-addicts, troubled youths and women who have been long-time recipients of aid for dependent children welfare.

In a field strewn with failures, the 30-month-old program in 15 locations around the nation is showing some success in helping members of the subculture increasingly called the under-class develop work habits and skills enough to propel them into the working class. Most of the people in the program are working as comstruction laborers or service personnel like janitors.

"It's a small breakthrough and we may have to settle for small breakthroughs with this class," said Mitchell Sviridoff, a vice president of the Ford Foundation, which helps fund the programs.

"The benefit-cost ratio for society of every individual success is very high - measured rot just by gains accruing to assisted people, but also by the reduced costs of crime, dependency and intergroup tensions," Sviridoff said in a speech.

William J. Grinker, who oversees the supported work program as president of the Manpower Demonstration Research Corp. (MDRC), said: "I would not have predicted three years ago the results we getting."

An unusual consortium of five federal agencies and the foundation have funded MDRC an the supported work experiments. The Labor Department is the key participant, but Justice Health Education and Welfare, Housing and Urban Development and Commerce also participate.

About 40 per cent of the funding comes through MDRC, about 30 per cent is raised locally by the operators of the 15 supported work sites and the rest is earned by the workers, Grinker said.

It costs between $9,000 and $15,000 a year per worker, including salary. The starting pay is $2.68 an hour and the top is $3.05 an hour. The program aims to keep workers earning about 78 per cent of the local wage for comparable work.

The Rev. Francis Schiller, who directs the Jersey City program, says a core of about 30 per cent of those who enroll don't want to work and the program does nothing for them.

In Jersey City, however, over 60 per cent of the workers have been placed in regular jobs after leaving the program - which they must do after a maximum of 12 months.

The argument is that the workers should not stay longer in supported work or it will become a cocoon and lose its value as a preparation for working in a competitive situation. Shiller agrees, but also points out the poignancy of the 5 to 10 per cent who perform well enough in the program but need it for something like it forever. They are pushed out at the end of their time in what gets called "the forced transition."

The Jersey City placement figure is about twice the 30 per cent success rate for the whole program, but even one-third is considered good because previous programs have usually completely failed to affect the underclass.

And the supported work planners who adapted their program from the sheltered workshops some European nations use to aid physically and mentally handicapped are confident of their figures because a large part of the program is a rigorous evaluation. A computer in Princeton, N. J., turned thumbs up or thumbs down on each early applicant. That random selection process provided a control group of rejected people who are being monitored for comparison with the performance of those accepted.

The present 15-location program followed the introduction of the idea in New York City by the Vera Institute of Justice, a New York foundation.

The program a four-year demonstration and it will be up to the Labor Department and its partners in the consortium to determine what happens when the demonstration ends in early 1979.

"If this were 1962, the next stage would be a national program," Sviridoff said of the days when social programs proliferated - and failed - rapidly. one example was the Model Cities program which was intended to be a demonstration, but that work was dropped in hasty reaction to the 1960's urban riots.

Sviridoff and others are wary of supported work's success creating political pressures for rapid expansion, but he is confident that the federal officials in charge are "aware of the importance of gradual development of the concept."

The supposedly unemployables are gradually given more stress as their months in the program pass, but some aspects of any job - like tax deductions and paychecks docked for hours missed - are present from the start.

Richard de Crescenzo, the Jersey City associate director of the Community Help Corp., said: "If you coddle them, they'll walk all over you."

"We do the non-Catholic school thing by keeping all of them," Schiller said in explaining that Jersey City has fired very few of its employees compared with other cities.

"When people steal from you not once, but a number of times or don't show up for days you do kind of think of turiong them loose." de Crescenzo said when asked about difficulties of supervisor the workers.

But he and Schiller cited with pride an IBM foreman loaned to teach some of their workers typewriter renovation who said he had never taught people so serious about learning.

"You get this down pat and it's a trade," Castro said at his bench in the typewriter shop. Asked why he and his buddies didn't quit the program he said: "Well you can if you wanta stay dumb all your life."