Maryland pharmacists who are asked to fill prescriptions for costly name-brand drugs would be permitted to susbtitute less expensive drugs with identical chemical composition under a bill approved today by the Maryland Senate.

The generic drug bill, and a similar measure approved by the House on Monday, would allow the druggist to make the substitution without consulting the prescribing physician, unless the doctor specifically prohibited the substitution.

The proposals were heavily supported during hearings by senior citizen groups, and also were supported by pharmacists. Some physicians opposed the bill, although the House version was sponsored by Del. Torrey C. Brown (D-Baltimore), the only physician in the legislature.

Dr. Brown testified that it makes little senset to require physicians to approve of the substitution because "doctors don't know anything about generic drugs." Other witnesses said that medical students are taught about brand name drugs only and do not know the chemical equivalents.

The bill, which replaces a weaker measure that would have required physician approval, does require the druggist to tell the patient of the substitution. If a generic drug is substituted, the pharmacist must use the lowest cost generic equivalent, and pass the cost saving on to the customer.

In another medical matter, the Senate approved and sent to the House a bill that would put the state's stamp of approval on the use of the controversial chemical laetrile, a substance hailed by proponents as an effective treatment for cancer but denounced as a useless placebo by most of the medical community.

Laetrile, an extract of apricot or peach pits, may not be transported from state to state because of a federal Food and Drug Administration rule. Doctors and cancer reserchers testified last month that laetrile does nothing to help cancer patients, and may induce them not to take orthodox medical treatments for cancer.

For most senators, though, the testimony of cancer victims who said laetrile has helped them was more persuasive. "This is a question of freedom of choice, a ray of hope for those individuals who have no other way to turn," said Sen. Edward T. Hall (R-Calvert), sponsor of the bill.

In other action, the Senate passed and sent to the House a bill that would alter the consumer loan industry in Maryland.

Maryland law now provides for two kinds of consumer loans: the small loan of up to $500, with a maximum interest rate of 36 per cent, and the consumer loan, with an interest rate of 18 per cent on a maximum loan of $3,500.

Because of a peculiarity in the way the interest rates for the two kinds of loans are legislated, customers of companies like Household Finance Co., which grant samll loans, are unable to get loans for amounts between $500 and $1,200 because they are not profitable for loan companies.