Rep. Claude Pepper (D-Fla.) will give up chairmanship of the House Select Committee on Aging to take over as head of the Rules Committee next year, congressional sources said yesterday.

The switch will put him in position to influence all legislation that goes to the House floor in the next Congress, including especially any bills to alter Social Security, of which he has become a leading and vociferous protector.

Sources said Pepper has informed House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) of his decision and received O'Neill's approval.

The Rules Committee, which in recent years largely has been controlled by the leadership, decides which bills approved by committees will go to the House floor and what amendments may be offered. It thus has the power to stall or enormously facilitate passage of any particular bill.

Rep. Richard Bolling (D-Mo.), present Rules chairman, is retiring at the end of this Congress and Pepper is next in seniority on the panel. But some had expected that the 82-year-old New Dealer and former senator from Florida, now the oldest member of the House, might choose to stay as head of the aging committee, where he has become a national champion of programs for the elderly. However, in contrast to the power of the Rules Committee the aging committee is basically a study group.

While giving up chairmanship of the aging panel, Pepper reportedly plans to stay on as a member. The next two Democrats on the roster are Edward R. Roybal (Calif.) and Mario Biaggi (N.Y.). The next most senior Democrat on Rules is Gillis W. Long (La.).