WHERE SHE WAS a student at McKinley High School, Rosalyn Brown used to think she'd be on top by the time she reached 25. The stars brightened during her days at Wilberforce University in Ohio. By 25, she'd be independent, carrying an attache case, have her own apartment, dropping by her parents' house for weekend visits.

Rosalyn Brown is 25 now, and her bachelor's degree hangs on her wall. But she hasn't been able to find a job that pays more than the minimum wage, $3.75 an hour or $7,800 a year -- about $200 a year less than a G8-L. She sees a lot of her parents, since she cannot afford to move out of the family house in the 4200 block of East Capitol Street in the Fort Chaplin area. She doesn't have an attache case. Just a purse full of employment applications.

Now comes the new conservatism and the proposals for a sub-minimum wage as a way of expanding job opportunities for young people.

You've heard the argument. It goes like this: There are a whole lot of young black people out of work, officially, more than 40 percent in this town alone. Some businessmen don't want to hire people because the minimum wage is too high. To solve the problem, you create incentives for businesses to hire, you allow them to get off the hook cheaper. It's a form of deregulation, as in ignoring the fact that the oil companies have been making record profits and allowing them to make more as an incentive for them to look for more sources of domestic oil.

Poor, unemployed and underemployed folks are supposed to love this sub-minimum wage. After all, a sub-minimum wage job is better than none, the argument goes.

Rosalyn Brown doesn't see how it would help. "It would hurt a lot," she says. "Employers simply would give the jobs to the people they wouldn't have to pay as much."

The National Urban League says she's right. The sub-minimum wage could mean the loss of a job for her and others even less fortunate than her.

"It would most likely result first, in the displacement of adults, particularly blacks, who are currently being paid sub-minimum wages in violation of federal minimum wage guidelines," concludes the league's Dr. Robert Hill. Advocates of the sub-minimum wage, he suggests, "may be less interested in hiring more teen-agers (whether black or white), than they are in eliminating, or severely undermining the minimum wage of all workers."

It is hard to believe that some employers wouldn't hire 16-to-19 year olds who would bring them lower payrolls than paying for the higher skills of older workers. And I'm enough of a skeptic in these matters to look at how much benefits cost and guess that employers might soon discover the advantages of hiring a string of short-term, cheaper teen-agers rather than more expensive, permanent adult workers. After all, benefit packages for long-term employes can add as much as 40 percent to payroll costs, while short-term workers cost less than half as much.

What we seem to have here is a general retrenchment on the part of the employers that flies in the face of the aspirations of young people like Rosalyn Brown.

And there is insult added to injury here. With few exceptions, blacks in this country still earn less than their white counterparts with comparable education. And the notion that what's good for business is good for the black community just hasn't worked.

Of course, a high minimum wage -- any kind of minimum wage -- takes its toll on small businesses, most of which operator on marginal resources, many of which in this city are owned by blacks. But the answer to this is to offer some help to small businesses -- which are collectively the largest employers -- not to return 16 and 19 year olds to slave wages in a time of high inflation and high unemployment.

Elizabeth Jones of the 14th Street Project Area Committee works with some of the city's forgotten youth. Some of them, at 18, often have a couple of children but with a chance to make it legitimately, want an opportunity to make life better for their children. She finds the proposal for a sub-minimum teen-age wage alarming.

"It would be a terrible thing if it happens," said Jones. "These kids are already frustrated to have to work at the minimum wage because they can't get something else. It would add to the frustration. You would have trouble. Don't hurt them anymore."