Colleges are scrambling for money to replace the federal funds being withdrawn from student aid. Students will feel the first real pinch in the 1982-83 school year, which starts this September.

Most of the replacement funds will come in the form of loans rather than grants, and at higher interest rates than you have to pay for federally subsidized student loans. Among the money sources on today's market:

1. Guaranteed cost plans, introduced a couple of years ago by Washington University in St. Louis, are now being widely imitated. Parents pay for four years of college in advance. In return, the school guarantees that their tuition cost will not rise. Many schools lend money at below-market interest rates to help parents make prepayments.

John Biggs, vice-chancellor for administration and financial affairs at Washington University, says that at present the prepayment program is open only to students who receive no financial aid. Of 400 to 500 students in that category, about 100 join the program each year. About 25 of them prepay out of their own funds--which the school then uses to help make loans to the other 75 students, at 13 percent interest and payable in up to eight years.

"The university will return any unused tuition if the student leaves before four years are up," Biggs told my associate, Virginia Wilson, but the parents will have lost the interest they paid on the money.

2. Colleges are drumming up more student-aid funds of their own. "They're having intensive alumni fund-raising drives," says student-aid expert Robert Leider. "And they're trying for corporate funds." Schools of special interest to business, like engineering schools, are getting the lion's share of corporate aid--hence may have more money on hand for needy students.

Some colleges are shifting money out of their maintenance funds and into the student-aid account. In a fair number of cases, money that might once have been given in the form of a grant becomes a loan. Colleges are going to need their aid funds back, to restock the pond for the next generation of students.

When a college fails to attract enough good applicants, it starts to offer special inducements, Leider says. Some will match any scholarship you already have. Some will give siblings a 25 percent discount on tuition. More schools are giving scholarships to bright students, regardless of parental income. For the latest list, write for Leider's "A's and B's of Academic Scholarships," $2.75, Octameron Associates, P.O. Box 3437, Alexandria, Va. 22302.

3. More colleges offer installment plans, where you pay on a monthly schedule (at perhaps 12 percent interest) instead of in two large semester lumps. The plans may include optional insurance that will pay for your child's education if you die or become disabled.

4. The insured tuition plan offered by the Richard C. Knight Insurance Agency in Boston, Mass., is for the parent who finds it hard to save large sums for college, but has a sizeable monthly income. You make monthly payments to the Knight agency, and Knight pays the big semester bills as they come due. Life and disability insurance is obligatory; it's where the company makes its money. There are also small start-up and maintenance fees.

Traditionally, Knight plans called for larger payments in the first year of the program and smaller payments later. But as college costs rose, parents found that arrangement harder to handle. Starting this year, Knight will offer a four-year level-payment plan, which includes some loans in the earlier years. When your account is in surplus, it will earn 5 1/4 percent interest; when it's in debt, you'll pay interest at 12 percent. It would cost you $475 a month (covering all costs) to fund a four-year tuition obligation of $5,000 a year.

5. An interesting new tuition reserve and deposit plan is now operating through the Citizens Bank of Dallas, Ga., and it hopes to sign up banks in other states. You deposit funds in a 5 1/4 percent passbook account, and are then allowed to leverage that deposit into a college loan. If you put in $8,000, for example, you can borrow $5,000 a year for four years, at 12 percent interest. You're given about seven years to repay, at $247 a month. For information write to the Citizens Bank at P.O. Box 186, Dallas, Ga. 30132. The bank accepts applicants from all states.