Dependent illegitimate children of deceased federal workers and retirees will be eligible for both retroactive and future monthly civil service survivor payments of about $135, and of government-paid health insurance through age 22 under legislation being proposed by the Carter administration.

The proposed bill, designed to put into effect a little-noticed order of the (civil action 78-317) U.S. District Court last fall, would extend eligibility for survivor benefits to any and all "recognized" illegitinate children in the future, and back through at least 1972. It is possible that the court may decide that the payments are due illegitimate children back as far as 1948.

Nobody has any idea how many individuals might benefit from the legal change, or what it will cost the government. But the rate of out-of-wedlock births nationally now stands at around 14 percent. In the District of Columbia, with its sizable federal employe population, records indicate that 53 of every 100 births are illegitimate.

The Office of Personnel Management (formerly Civil Service Commission) recommended the legislation to put existing federal rules in conformity with the U.S. District Court ruling which is now the law of the land. The court, in effect, ruled that the government could not deny survivor benefits to illegitimate children simply because they did not live with the federal parent, or because the parent did not contribute more than half the child's support.

Federal officials say that even if Congress does not approve the proposed legislation, they are preparing to honor the court order. One of the cases in the decision would make the government liable for payments denied illegitimate children as far back as 1948. The court must set the date.

Government officials say that to be eligible for the survivor benefits and health coverage, the dependent child would have had to be "recognized in some way" by the employe or retiree before his or her death. That, they say, could have been established in a paternity or support hearing, or even under common law if the individual acknowledged to friends and associates having an illegitimate child.

Currently, there are 77,000 "dependent" children on the civil service retirement rolls. Their average monthly payment is $135, ending at age 18 unless the child remains in school, in which case it ends at age 22. Federal officials say they have no way of knowing how many of those 77,000 are illegitimate, but they speculate that the number is rather small because of tougher eligibility regulations before the court made its ruling.

Meantime, federal retirement officials are braced for a deluge of claims from children, some of them now in their 30s, asking for retroactive benefits because they are the illegitimate offspring of a deceased federal worker. Uncle Sam maintains retirement records on 15 million persons, and the government may have to advertise, asking claimants to come forward to present cases of back-benefits and payments due them.