A pacifist couple has received a $4,741 refund on their 1982 federal taxes after objecting to contributing to national defense spending, but Internal Revenue Service authorities indicated today that they won't get to keep it.

In fact, the IRS said, in such cases the taxpayer usually has to pay interest on the refund, plus a $500 "frivolous" tax return penalty as well. Officials blamed the issuance of such disallowable refunds on the crush of work on IRS clerks.

Last April, Joseph and Barbara Jensen of Baltimore filed an ordinary tax return, except that they claimed a credit for $4,741.32--about half the tax due on their income. They attached a letter saying that "divine law" prohibited them from contributing toward military spending and that by their reckoning about half the U.S. tax-supported budget goes to national defense.

In August, the couple received a refund check from the IRS for $4,741. "We immediately gave it away to peace groups and places that feed the hungry," said Barbara Jensen, 33, an administrator in the Maryland Department of Health and Mental Hygiene. " . . .We feel it is immoral to pay for killing people, and an awful lot of the U.S. budget is going to killing people."

IRS officials, who are prohibited from discussing specific cases, said today that tax credits or deductions claimed on grounds that the money should not be spent on national defense or other specific budget items are automatically disallowed.

What happens, however, a spokesman said, is that in the avalanche of returns received by the IRS in April, clerks don't have the time or authority to single out and examine "fishy looking" returns, but simply flag them for an auditor to look at later.

"If the arithmetic is right and the taxpayer asks for a refund, he gets a refund," the spokesman said. Then if an auditor later finds an improper deduction or credit, the taxpayer is notified and directed to return the refund plus interest and, in some cases, a "frivolous" return fine.

Barbara Jensen said today that she and her husband have received a $500 "frivolous" penalty but have not yet been directed to return the refund or interest on it.