Money invested in the multimillion-dollar federal employe thrift savings plan will earn 9 5/8 percent interest this month, a jump from the 9 percent the fund was earning in September.

Nearly a million of the government's 2.9 million employes now have thrift savings accounts. They are similar to tax-deferred 401(k) savings plans that are available to many private-sector workers, although the government plan allows employes to invest more and get a bigger matching contribution from the employer.

The federal thrift fund was worth $772 million as of yesterday and is growing at the rate of $5 million a day.

Federal and postal workers who are covered by the new Federal Employees Retirement System can invest up to 10 percent of their salary (or a maximum of $7,000 this year) in the savings plan. Those who put in 5 percent or more get a matching 5 percent tax-deferred contribution to their accounts from Uncle Sam. Workers who are covered by the old Civil Service Retirement System (most people hired before 1984) can invest 5 percent into the tax-deferred plan but do not get any matching contribution from the government.

Employes who convert from the old pension plan to the new FERS system can immediately raise their contribution rate. The next open season for other employes to join the savings plan, increase or decrease contributions or withdraw from it, begins Nov. 15.

All money invested in the fund this year goes into medium- and long-term Treasury Department securities. Next year workers who are covered by the new retirement system can begin splitting their investments between that fund, a fund with a fixed investment rate or a stock market fund.Meetings

National Association of Retired Federal Employees Arlington chapter meets at 1 p.m. Wednesday at the Culpepper Garden Recreation Center. Guests include state Sen. Edward M. Holland (D-Arlington) and his Republican opponent, Joseph Vasapoli. For information call 528-1020.

NARFE's Springfield chapter will meet at 1:30 p.m. Wednesday at St. John's United Methodist Church.

The professional development program of the Training Officers Conference will be Tuesday at the Fort McNair Officers Club. For information call 475-5170.Job Mart

International Trade Administration is looking for a Grade 9 ($22,458) writer-editor with promotional and advertising copy skills, and a GS 7 ($18,358) editorial assistant. Call 377-4919.

Park Police jobs: The wrong telephone number appeared in yesterday's item about the $20,556 openings for police officers. The correct number is 485-9790. Applications must be in by Oct. 16.Police Raises

President Reagan is expected to sign legislation that will mean phased catch-up pay raises for Library of Congress police officers. The bill by Rep. Mary Rose Oakar (D-Ohio) will boost salaries of Library of Congress police privates, who now start at $18,358, to the same level as police privates of the U.S. Capitol Police. They start at $21,733. Under the bill the Library employes with get one-quarter of the raise this year, one quarter next year and so on until their pay is on a par with their Capitol Police counterparts.