Senate Republicans, outnumbered on Capitol Hill and facing an incoming Democratic President, are preparing for legislative battles with the Carter administration by changing the staff and the mission of the Senate Republican Policy Committee.

If the committee turns into the forge of ideas and policy alternatives enisioned by Chairman John Tower (R-Tex.), who is making the changes, the Republicans will be able to field a much tougher force against President Carter and Senate Democrats. At the same time, Tower will gain a higher profile in the GOP leadership.

Convinced that the committee staff has failed to generate the policy initiatives and thrust needed by the minority, Tower has told intimates that the staff needs "new blood." "I want to get top-notch professionals to produce policy papers," he said recently.

His first step has been to hire Max Friedersdorf, President Ford's congressional lobbying chief, to replace Edward (Ned) Beach as staff director.

In the past, Tower said, Senate Republicans tended to take their policy leads from the Republican White House. But with a Democratic President coming in, "now we have to take our own initiatives . . . The staff will develop ideas. Sometimes, perhaps, in support of the President, more usually in opposition," he said.

Outside the Senate, few have heard of the policy committee. But it has a $422,800 annual budget from the Senate, 16 employees, and offices in the Russell building. Five of the staff are paid in the $37,500 to $39,000 range. The staff's function has been research, vote analyses, and summaries of legislation for the use of GOP senators.

The incoming staff director, Friedersdorf, 47, was a midwest newspaperman for 10 years before going to work for Rep. Richard L. Roudebush (R-Ind.) for another 10 years starting in erty program as its lobbyist on the 1961. Then he moved to the antipov-Hill under the Republican administration in 1971 and finally to the White House lobbying staff which he headed for the past two years.

Beach, 58, is a graduate of the Naval Academy and a former career officer. He joined the policy committee staff as director in 1969. Beach, a well-known historian and author of several books, including "Run Silent, Run Deep," is eligible for a pension. He said he intends to keep on writing.

The fact that he was bumped to make way for Friedersdorf isn't going to hurt him, but the other 15 members of the staff are in danger of losing their jobs.

"I've given Max pretty broad leeway" in hiring and firing, Tower said recently. "But nobody's being purged, and you can't go on the assumption that everybody is going." He conceded, however, that many of the present employees may be dropped.

What will happen, both Tower and Friedersdorf said, is that current staffers who want to stay will be interviewed and considered for retention if it appears they fit into the new scheme.

One high-paid employee, Bill Hatch, had decided to retire on a disability pension, but that decision was apparently made before the reorganization.

So far, it appears that only one high-paid employee, Joan B. Baldwin, definitely will be retained, according to Senate GOP sources." Her performance has been very very good," said one Republican.

Friedersorf has already interviewed all the other employees, including two of the highest paid - Bruce R. Barr, 41, who has been with the committee 15 years and is an economic specialist, and Martin J. Clancy, 57, who has been there nearly 16 years - to see if he should keep them. But he has made no decisions except on Baldwin.

Friedersdorf said he will probably bring in as his deputy Robert Wolthius, a former top aide to ex-Sen. Wallace F. Bennett (R-Utah), who has been working with him at the White House. "He's a Phi Beta Kappa and a Ph. D," Friedersdorf noted.

Some of the Senate's more liberal Republicans like the idea of what Tower is doing but fear Friedersdorf.

"He's pretty conservative," said one who asked not to be identified.

The GOP policy committee isn't the only place where there could be major changes.

The Democrats also have a policy committee with the same budget, already structured along the lines Tower is seeking.

But virtually everyone there, from chief counsel Charles Ferris down, is a "Mansfield man," put there by retiring Majority Leader Mike Mansfield (D-Mont.) during his 16 years as leader.

The Democratic committee staff under Ferris served as an intellectual factory to produce policy initiatives and concepts for Mansfield, and as "the neck of the bottle" in the flow of proposals from academia and hundreds of legislative assistants elsewhere on Capitol Hill.

With Mansfield leaving, however, there will be a new Democratic leader - the frontrunner is Robert C. Byrd (D.W. Va.) - and it's likely there will be some personnel changes. Ferris, one of the most respected staff men in the Senate, was called to Plains, Ga., recently for an interview with President-elect Jimmy Carter and appears slated for some job in the new administration.

Byrd would then in all likelihood bring in one of his own men, perhaps James H. Duffy who was longtime counsel to the Senate Rules Subcommittee on Privileges and Elections but now works for Byrd in his assistant leader capacity, or Tom Hart, a staff member on the Judiciary Committee.