If there is a place in the "Guinness Book of World Records" for successfull direct-mail fund-raisers, the National Association of Retired Federal Employes ought to qualify.

NARFE, with a conservative, thrifty membership of about 300,000, has managed to raise $800,000 from a single letter fund appeal. Most of the donations came within a 30-day period.The NARFE mailroom has still not recovered from the welcome onslaught.

The federal-postal retiree group warned its people of plans to merge the federal retirement system with social security. Its letter to members said a legislative war chest would be needed to fight the merger plan on Capitol Hill.

Within less than a month, NARFE, which often has trouble collecting a few dollars in dues from its fixedincome members, struck gold.

Federal and postal unions -- whose members have a lot more spendable income -- are green with envy. NARFE was instrumental last session in blocking merger of the two systems.

Instead of marrying the two very different retirement plans, Congress agreed to first have a feasibility study of the pension tie-in. Although that study -- and others -- is not due until the end of this year, legislation already has been reintroduced in Congress to require federal workers to come under the social security system.

Meantime, the General Accounting Office says that Congress ought to do a better job of managing the 38 different retirement systems the government now runs. GAO says the plans cover 5 million people and pay out more than $15 billion a year to 2.5 million retirees.

Although income to the fund still exceeds outgo by a comfortable margin, the price of early retirement benefits, inflation and regular cost-of-living adjustments to retirees has produced an unfunded liability, GAO says, of $273 billion for all the funds.