One of the best ways for federal employees to safely ride their investment roller coaster is to check the constantly changing payoffs of the three tax- deferred investment options available through their thrift savings plan. What you see depends on when you looked. For example:

Last year, the popular C-Fund (stock market option) paid 31 percent.

But as of today, its rate of return (over a 12-month period) is down to less than 11 percent.

For the 1989 calendar year, the C-Fund had a healthy 31.03 percent rate of return. The F-Fund (bond market option) paid 13.89 percent. The safer G-Fund (treasury securities) paid 8.81 percent.

For the 12-month period ending in March, the C-Fund's rate of return had dropped to 19.16 percent. That reflected more recent downturns in the stock market that didn't affect 1989 earnings. The F-Fund return was 11.37 percent, and the G-Fund was 8.64 percent for that period.

The latest numbers, for the 12 months ending in April, show the C-Fund payoff had dropped to 10.46 percent. The F-Fund had dropped to 8.10 percent, falling behind the payoff of 8.59 percent for the treasury securties G-Fund.

People who can invest in the stock and bond funds (which are open only to the 900,000 workers in the new Federal Employees Retirement System pension plan) should be aware of the ups and downs of those two funds compared with the steady, safe G-Fund, which is open to all federal workers.

The open enrollment period for the current savings plan season runs through July 15. People

Corinne Proctor is retiring after 31 years with the Department of Transportation. Among other things, she was in charge of changes in the department's organizational manual. Friends are giving her a luncheon Friday at the Bolling Air Force Base NCO club.

Dalmer Hoskins has been elected secretary-general of the Geneva-based International Social Security Administration. He's been policy development director of the Social Security Administration since 1987.

Randall P. Shumaker has been named superintendent of the Naval Research Laboratory's information technology division. He's been acting superintendent for a year. Job Mart

The Treasury Department has openings for computer specialists at the Grade 12/13 level. Call 566-5411.

The National Credit Union Administration needs a GS 11/12 attorney-adviser. Call Deborah Tolbert at 682-9720.

The Centers for Disease Control has an opening in Hyattsville for a GM (merit pay) 13 computer specialist. Call Lula Murphy at (919) 541-4420.

The Office of Personnel Management wants a GS 11/12 medical analyst. Call 606-2745.June Meetings

The VA Alumni Association will have its June 22 luncheon at the Arlington-at-Ballston Holiday Inn. Cyril Brickfield, former executive director of the American Association of Retired Persons, is the scheduled speaker. For details call Eva Zbel evenings at 893-7294.

The National Association of Government Communicators' after-work social will be June 12 at the National Press Club. Call Barbi Richardson at 724-0790.