The Senate and House today are expected to take major steps toward putting future federal workers--including members of Congress and presidents--under Social Security.

This morning the House takes up the complicated Social Security reform package, which has the blessings of its Democratic leadership as well as the White House. One portion of the measure--which may be debated again tomorrow--would require that anyone coming into government after next Jan. 1 be covered by Social Security as well as the civil service retirement system.

If the reform package becomes law those new feds would have to pay into Social Security (6.7 percent of salary on amounts up to $37,500) as well as 7 percent of gross salary as their contribution to the government's in-house retirement program.

Current federal employes would not be put under Social Security, although they would be required to keep paying the 1.3 percent Medicare tax.

On the other side of the Capitol, the Senate Finance Committee today is expected to begin a final markup of a similar Social Security financing plan. It also contains mandatory coverage for feds hired next year.

Federal and postal unions have been desperately trying to block, or at least delay, mandatory Social Security coverage.

The House Rules Committee-- which acts as the legislative traffic cop for the House--yesterday rejected a plea from Rep. Mary Rose Oakar (D-Ohio) to let the House vote separately on an amendment to delay Social Security coverage for feds until 1985.

Organizations representing the 2.8 million U.S. workers and more than a million retirees have mounted their most impressive--and expensive--lobbying effort on the Social Security issue. They argue that putting new feds under Social Security will cut off the flow of new contributions to the federal retirement program and ultimately wind up costing the taxpayers more.

But congressional leaders--eager to deal with the Social Security problem before the 1984 election year--say action must be taken taken this year. Some of them have criticized the unions' advertising campaign on radio, television and in newspapers, saying the ads "misrepresent" the threat to the federal retirement program. The program will continue to be funded by government and employe contributions, the leaders maintain.

Pro-federal worker legislators have promised to come up with a modified civil service/Social Security retirement plan with benefits and contributions that are roughly comparable to the present system. The "roughly comparable" part is what worries the unions.

Today on the Senate side the Finance Committee will begin writing its final version of the Social Security financing plan. It also calls for putting new feds under Social Security next year.

Organizations representing civil servants and retirees have mounted an extraordinarily vigorous lobbying effort around the Social Security issue. Last week a group of postal workers staged a sit-in at the office of House Speaker Thomas P. O'Neill (D-Mass.), who supports the bipartisan social security package.

The American Federation of Government Employees (AFGE) has 2,500 members in town today. They are here to lobby against mandatory social security, and White House plans to drastically overhaul the federal retirement program and freeze federal pay this year.

President Reagan's plan--which has not yet been sent to Congress--would cut annuities of federal workers who retire before age 65. Employes now can retire at age 55 with 30 years service with an annuity equal to about 56 percent of salary.

Reagan also wants worker contributions to the retirement program (now 7 percent) increased to 11 percent by 1985.

Unhappy AFGE members plan to pack a House Civil Service subcommittee hearing this morning where Office of Personnel Management chief Donald J. Devine is to be the first witness. He is the chief architect of the administration plans to change federal pay and retirement policies.

AFGE President Kenneth T. Blaylock is scheduled to testify after Devine.

All in all, this may be a very long day for politicians on both sides of the Social Security issue.