Most Americans who plan to send their children to college are worried that they won't be able to afford it, and nearly half oppose any further cutbacks in federal student aid, a nationwide survey says.

Fifty-four percent of the parents with such plans said they were very concerned that they would not be able to finance that education, according to the poll. Another 32 percent said they had some concern, but probably would be able to pay the bill.

Only 11 percent are confident that they can pay for four years of college.

The survey of 1,188 adults, conducted for the American Council on Education and 10 related groups by Group Attitudes Corp., comes as the Reagan administration has cut more than $300 million from four of the largest federal student-aid programs, and has proposed that three of these programs be phased out next year.

"If everything's being cut, we can be cut and we could live with it somehow," the Rev. Theodore M. Hesburgh, president of Notre Dame University, said at a briefing. "We could stand a little belt-tightening . . . . But the one thing people don't want to see cut is the money that would allow needy students to go on to higher education."

Hesburgh said that if the government doesn't help ghetto youngsters learn to compete in an increasingly technical society, "they may simply be unemployable."

More than 70 percent of those surveyed favored continued federal grants to poor students, while three-quarters said the government should keep providing low-interest loans to middle-class students.

A majority also supported federal aid for academic research in medicine and science. But the poll did not address the question of taxes or how these programs would be financed.

Still, many said that federal aid to higher education should not be exempt from budget cuts. While 44 percent said these programs should not be cut at all, 40 percent said they should be reduced somewhat and 15 percent favored drastic cuts.

People earning $40,000 or more were twice as likely to support substantial cuts than those making less than $15,000.

While three-quarters of the respondents rated higher education in the United States as excellent or good, few believed it provides any guarantee of a job. Nearly two-thirds said a person with a college degree is just as likely as one without to be unemployed in a recession.

A majority said that some students don't go to college because it is too expensive or not as attractive as job-training programs. Others said that some people just don't like school.