Cash -- that non-plastic money once used to buy things -- is making a comeback. Since the Federal Reserve Board Clamped on credit controls in mid-March, consumers and merchants alike have shown a renewed interest in currency and checks.

These folding funds got a boost yesterday when the House Banking Committee unanimously agreed to lift restrictions against discounts for cash payments. Under the Truth in Lending Act, Sellers are prohibited from offering more than a 5 percent discount off the posted price for paying in cash. By the same token, they are not allowed to impose a surcharge on credit card users.

Declaring that the United States has been for "too long a nation of credit card junkies," Rep. Frank Annunzio (D-Ill.), the sponsor of the committee-approved bill, called for a return to cash and carry. Letting merchants decide for themselves how much of a discount, if any, to offer to customers paying in cash, check or ways other than credit card or openend credit plan would fight inflation and reduce regulation, he said.

The Fed, which had received many inquiries from retailers seeking clarification of the discount law, supported the bill. So did consumer and labor groups. The American Bankers Association, representing many credit card issuers, opposed it.

Later, the committee voted 22 to 16 to shelve a bill, opposed by the Fed-and the ABA, prohibiting creditors from changing terms retroactively and requiring them to give 60 days notice before making future changes.

Creditors such as Citibank and Montgomery Ward already have announced increases in annual fees or minimum monthly payments or interest rates. The new charges usually are applied to existing balances as well as new purchases. Thirty days notice now is required.