The inmates of federal prisons have lost a perquisite they used to share with members of Congress and federal bureaucrats: free mailing privileges.

To some, the ideal of unlimited free postage for prisoners is a civil liberties issue. For other, it's an outrage. In any case, the Bureau of Prisons has concluded that such a privilege for prisoners was a mistake.

Beginning in 1976, according to bureau officials, abuses of this privilege -- which includes free stationery -- began to multiply. According to the Federal Register of June 30 (page 44220), some inmates were mailing "the same letter to each member of Congress." Others ordered junk mail from mail order firms. One group of prisoners got the names and addresses of "recent widows" from newspapers and wrote them "stating that their deceased husbands owed them money."

The last straw apparently was the inmate who announced he was running for president of the United States and sent out more than 150 letters, under the free privilege, soliciting money for his campaign.

The Bureau of Prisons administration, sparked by the growing cost and embarrassment of the letters, announced a year ago a new set of interim rules that sharply limited the free mail. Thereafter, prisoners would only get five stamps per month free. If a prisoner wanted to write more than five letters, he could buy additional stamps from the prison commissary with his own money.

Protection was given mail sent to lawyers and to the courts. When an inmate did not have money to pay for stamps for these letters, the prison would pay the postage.

Over the past year, comments have poured in on the interim rule -- interim because it went into effect June 19, 1979, but was not considered final.

Many prison reform groups and individuals protested the stamp limitation, saying it "restricted the right of an inmate to maintain contact with family, friends and others."

"It may contribute to the break-up of the family," another group commented. "The policy may be counterproductive to the bureau's efforts to return to the community productive and law-abiding persons," said a third.

However, other voices were heard. One comment suggested "that providing free postage and writing materials to convicted felons, but not to free world citizens, may violate the equal protection clause of the U.S. Constitution." c

Meanwhile, some prisoners found a way to misuse the one free mail privilege left -- letters to lawyers. According to the prison bureau, "an inmate at one institution [received] during a one-month period 600 free stamps for legal mail and/or administrative remedy filings."

The final rule, which went into effect June 30, retains the five-stamp limit but permits individual wardens to impose their own restrictions on free legal mailings "to prevent abuses."

In less than a year, the Bureau of Prisons bill for inmate stamps dropped from the "free" level of $1.4 million to about $600,000, according to agency officials. For comparison, the congressional franking in his election year is expected to cost $51 million, up over $10 million from 1979's nonelection-year level.