Cambridge, Mass. — Half of all black teen-agers who are out of school are looking for work, but can't find it. Why? One important reason, the latest research shows, is that employers have preferred to hire white women entering the labor force in increasing numbers. White women have won store-clerk, restaurant-employee, supermarket-checkout, and other service jobs that might otherwise have gone to young blacks leaving high school. Older blacks have also lost jobs to the women joining the work force.
Moreover, the influx of white women has depressed the wages of black men.
However, black males' job prospects have not been hurt by immigrants, either Hispanic or non-Hispanic.
These are some of the startling findings of a major research project of the National Bureau of Economic Research into the problem of high black unemployment in the heart of many of the nation's cities.
Other findings include:
* The theory that ''space, not race'' explains the high jobless rate in the nation's ghettos has been disproved. At least in Chicago, blacks living in an area in the city's West End near to plentiful suitable jobs suffered about as much unemployment as those in a ghetto in the south of the city far from appropriate work.
This damages President Reagan's free-enterprise-zone concept, says Harvard University's David T. Ellwood. ''Any hope that these (enterprise zones) will make a big difference (in black unemployment rates) is not well founded,'' he says.
Nor does the location of corporate manufacturing plants in ghettos make much sense - unless the companies practice strong reverse discrimination - that is, favor the hiring of blacks over whites, this research indicates.
Several companies, such as Digital Equipment Corporation and IBM, have purposely set up plants in black areas with the social goal of relieving unemployment partially in mind.
* Even in the nation's worst ghettos, some black young men ''escape the inner-city mess.'' And one of the surest routes out is to attend church regularly.
Richard Freeman, head of the research project, isn't sure why church-going black young men are much more likely to have steady jobs, higher income, use less alcohol or drugs, and have lower crime involvement than their peers. But the Harvard University professor figures it is partially the moral attitudes taught in church and partially the connections the youths make in church.
Boy scout membership also helps these youths improve their lot.
Mr. Freeman figures at least half the black young men in the most awful poverty tracks are trying hard through legitimate means to escape from their grim socio-economic backgrounds.
* Black young men want to work just as much as white youths. They have very similar aspirations for jobs and pay levels. However, they have less success in reaching these goals, perhaps because of racial bias, poorer backgrounds, or other factors. As a result, they often take dead-end type jobs, usually quit after a short time, and are unemployed for longer periods than their white counterparts.
* As compared to their prospects for good jobs, crime pays for many of these ghetto blacks, and many of them grab the fast-buck ''opportunities.'' In the language of Duke University's W. Kip Viscusi: ''The criminality among those who are not in school or employed is very sensitive to economic incentives. Since this group is responsible for most of youth crime, there is a major, economically responsive component of the criminal population.''
* Black youths in welfare families do more poorly in school or work than those in nonwelfare families, even when other factors are taken into consideration. Moreover, and this is a controversial finding, black teenage girls in welfare families are more likely to become unmarried mothers, apparently because it is economically feasible, perhaps even economically desirable.
''The black community,'' noted Robert I. Lerman, a research associate at Brandeis University's Heller Graduate School of Social Welfare, ''is only now starting to address in a serious way the unmarried-mother issue.''
The National Bureau research project is built around a survey of 2,358 minority males, aged 16 to 24, from low-income familes in Chicago, Philadelphia, and Boston. It was conducted during the 1979-80 academic year by Mathematica Policy Research Inc. of Princeton, N.J. But the research results are only now being published. Some 12 papers on the problem were discussed at a conference here last week, and Mr. Freeman was encouraged at the output of ''interesting explanations'' for high black-teen-age-male unemployment. ''We don't need to look at this problem as a black box (a mystery) now,'' he said.
At the same time, however, the findings of the research offer no easy solutions.
For instance, George Borjas, the University of California, Santa Barbara, economist who did the research on blacks and white women, figures the participation of white women in the labor force could rise even further, say from the current 50 percent to 55 percent. ''It would not be unreasonable to expect that,'' he says. So white women could continue to offer employers an alternative to blacks, who as one economist put it, appear to them ''to be a threat and talk funny.''
Nor do many economists have much faith in the ability of the government to remedy the lack of jobs for youths with work programs. ''They have not succeeded ,'' Mr. Freeman said.
The National Bureau of Economic Research refuses to make policy recommendations in its research. But Mr. Freeman personally thought it might be possible to provide some of the getto youths who want to get out of their plight with good jobs, training scholarships, and so on. Those programs may well cost taxpayers less than the costs of crime, such as keeping black youths gone astray in jail and extra police wages.
Further, he suggested that the black community should strengthen its legitimate organizations, such as churches and Bly Scouts, that have proven their ability to help.
In other words, possibly "bootstrap" operations in the black community and among black youths themselves offer the greatest promise. The research also shows that for those young black men who do persist in going to school or in getting further training, the relative pay-off in better-paying and more-secure jobs is greater than that for white youths with equivalent education and training.