The U.S. government is preparing to take nearly half a billion dollars from its own employe pension fund to pay full costs of attractive early retirement benefits, and double-decker annuity transfers for thousands of workers in the Panama Canal Zone.

Studies prepared for Rep. Gladys N. Spellman (D-Md.) indicate the federal civil service retirement fund would have to pay out at least $12 million a year -- for the next 30 years -- to finance the special retirement deal. It is part of the treaty transferring the Canal Zone from U.S. control to Panama.

Those extra retirement benefits -- not available to federal workers in the U.S. -- would permit canal employes to retire with as little as 20 years service, even if offered a comparable job nearby without loss of pay. Workers who took the early retirement would get pensions for life, and benefits would continue for their survivors.

Panamanians who did not elect to take the attractive early retirement could switch over to similar jobs under their nation's social security program. They would be allowed to transfer 14 percent of annual salary -- doube the amount refunded to U.S. federal workers who leave the retirement system -- into the Panamanian program.

When U.S. federal workers leave government service prior to retirement age, they can recover all the money they paid into the fund. That amount is equal to 7 percent of gross salary. The Panamanians would get double that amount, all of it coming out of the U.S. government workers' pension fund.

Spellman plans to take her Employee Benefits Subcommittee to Panama for three days of hearings beginning March 15. Chairman James M. Hanley (D-N.Y.) who heads the full Post Office-Civil Service Committee, will lead the congressional delegation.

Members are concerned about what some call a "raid" on the federal pension system, and the cost of early retirement to the fund. (Early retirement benefits already available to some U.S. federal workers are costing the fund an additional $1 billion a year, according to congressional actuarial studies). The price for the Panamanian payout would be higher, and could set the precedent for similar, costly early retirement breaks for U.S. workers.

Thousands of U.S. and Panamanian workers will lose their present jobs when the treaty goes into effect this fall. Many -- mostly Panamanians -- will be offered similar jobs with their government, or with successor agencies. U.S. workers will be offered similar early retirement benefits, some will get job offers in the Canal Zone and others positions offered back in the states. But the legislation proposed by the Carter administration would let employes decide whether to take jobs, transfers or retire early.

Many members of the Post Office-Civil Service Committee have no objection to the early-retirement benefits being offered as part of the treaty. They realize this is a very special situation that is not likely to happen again. But some are concerned that the bill for the extra benefits will be handed to the federal civil service retirement system. They would like to see the price come from the general revenues of the Treasury, since the treaty affects everyone.

"If the Senate approved the treaty in the name of the American people," one member said, "then the cost should be borne by everybody. It isn't fair to take the civil service retirement fund -- a private plan for people who happen to work for the U.S. government -- and tell it to pay the tab."

The final price tag, the liberalization of benefits and the decision as to who gets the bill -- federal workers or the entire pubic -- will be decided in large part by what the subcommittee learns later this month in Panama.

About That Mail Service: A lot of the complaints about poor mail service these days are coming from postal workers. Despite the fact that W-2 tax withholding forms were mailed out last Saturday -- according to the postmaster general himself -- many workers said they still had not received their forms as of yesterday.