The House Post Office-Civil Service Committee shortly is expected to reject all of the civil service "reforms" in President Reagan's budget, including the plan to raise the federal retirement age from 55 to 62.

For the last five years the Democratic-dominated panel has acted as a legislative roadblock to most of the civil service changes sought by the administration. The committee is expected to adopt a recommendation of its compensation subcommittee rejecting all the retirement changes proposed by the president and giving federal workers a 5 percent raise in January.

Once the committee approves a package it will be sent as a recommendation to the House Budget Committee, which is preparing an alternative to the president's budget for the fiscal year that begins in October.

Reagan's budget calls for a 3 percent federal pay raise in 1987, 1988 and 1989. He also wants civil servants -- who now contribute 7 percent of salary to their retirement fund -- to start paying 9 percent next year.

The president is again asking that the earliest government retirement age be raised to 62. Employes may now retire without penalty at age 55 with 30 years' service. His plan, which must be approved by Congress, would reduce annuities 2 percent for each year an employe retired under age 62. Workers who are 55 or older at the time of enactment would not be affected by the change.

The committee also is expected to reject the White House health insurance voucher plan. Under that proposal, government workers and retirees would get a check each year to buy health insurance. Currently, the government pays about 61 percent of the average premium. Insurance Refunds

President Reagan has until Tuesday to act on a bill allowing retirees to get the same 1985 health premium refunds as eligible federal workers. Congress approved the bill several weeks ago but did not send it to the White House until Friday.

If, as expected, the president signs the bill, insurance companies will begin the process that will lead to refund checks ranging from $17 to nearly $400 being sent to more than 2 million active duty workers and retirees. Letter Carrier Lobbyists

The National Association of Letter Carriers has its top state lobbyists in town for a seminar on budget-cutting plans that threaten the pay and fringe benefits of civil servants. The delegates also are getting practical experience in buttonholing legislators to ask them to oppose the president's plans. Meetings

U.S. Information Agency's Alumni Association will hold its March 6 luncheon at the Fort McNair officers club. USIA's deputy director, Marvin Stone, former editor-in-chief of U.S. News & World Report magazine, will speak. For reservations contact Fred Hawkins, 5214 Brookeway Dr., Bethesda 20816.

The American Society of Military Comptrollers' Washington chapter will hold its spring symposium March 31 at the Marriott Crystal Gateway Hotel. Speakers include former Environmental Protection Agency administrator Anne Burford, House Budget Committee Chairman William H. Gray III (D-Pa.) and presidential assistant Ralph Bledsoe. For information call Maj. Kitty Wallace, 695-2256. Job Mart

The Federal Home Loan Bank Board needs Grade 7 through 12 computer systems programmers (with VAX experience). Must have civil service status. Call Janice McMillian at 377-6063.