If you're making good money and still can't afford to pay for college, you're not alone. In what colleges call "the middle-class melt," some middle-income students are quietly slipping out of the pricier institutions -- high-cost public universities as well as private schools -- and enrolling in colleges that cost less.

Although not widespread (at least, not yet), the melt reflects a painful squeeze on incomes. From 1980 to 1988, family incomes rose only 53 percent, compared with a jump of 100 percent in the cost of private colleges. The sticker price of a four-year private school now averages $13,544 a year (apart from the discount for student aid), with the costliest schools in the $22,000 range.

The rate of increase in public institutions hasn't been nearly as high, although still greater than parental incomes: up 68 percent from 1980 to 1988. Public institutions average $4,970 a year for students who live within the state. But those prices, too, are being fiercely resisted by families of lesser means.

The dimensions of the middle-class melt show up in a study headed by Williams College economist Morton Owen Schapiro. Partly, the drop is due to the change in income distribution. There's a smaller middle class today than there was in 1978 (defining "middle" as families now earning $40,000 to $60,000).

But both the costlier private colleges and public universities are losing more of these students than their share, Schapiro says. Some are going to lower-cost private schools. Many are choosing local public colleges, whose prices are especially low.

So far, only the "middles" have been moving to the cheaper schools. Schapiro found no change at all in the proportion of lower-income students at the costlier colleges and universities -- thanks to those schools' rising budgets for financial aid. The gaps in enrollment left by the dwindling middle classes have being filled with higher-income students who can pay the freight.

College aid is available to kids in the middle. In fact, parents greatly underestimate how much help the costlier colleges are prepared to give. Still, the grants aren't enough to spare the families an elephantine loan, which appears to be the sticking point.

The able upper-middle-income student is increasingly found in the "public ivies" -- the better public universities. These include, among other schools, all the campuses of the University of California, Miami University at Oxford, Ohio, the University of North Carolina at Chapel Hill, the University of Texas at Austin, and the University of Virginia at Charlottesville.

The private colleges are getting the message. "In the future, costs shouldn't rise much more than the general inflation rate, and perhaps a little below," as opposed to the 9 percent to 10 percent price hikes of recent years, says Timothy Light, president of Middlebury College in Vermont.

While the private schools may be charging too much, some of the public ones are charging too little. Low tuition is fine, as long as the state allots enough money to education. But for years, New Jersey's legendary resistance to taxes has condemned Rutgers University to second-class status. "Of what real worth is a low-tuition policy," wrote Rutgers's former president, the late Edward Bloustein, "if it dooms students to an education below the quality they want and require?"

The percentage of higher-income students that the state systems serve is increasing at a phenomenal rate, says Arthur Hauptman of the American Council on Education. Given this changing population, more states should start playing the Robin Hood game: increasing their sticker prices, discounting rates to low-income students and using the rest of the money to raise the quality of their schools.

The middle-class melt and the gentrification of public universities are still in their very earliest stages. But these trends will intensify as the children of the burdened baby boomers reach college age. For the academics, it's a wake-up call. In the 1990s, they'll have to be affordable and good.