The most far-reaching reorganization of the Senate's sprawling committee system since 1946 won 9 to 0 endorsement yesterday from the Senate Rules Committee. Floor debate starts Monday.

The plan, though much less sweeping than originally sought by sponsor Adlai E. Stevenson (D-Ill.) and a special study committee, makes substantial changes. In an effort to streamline operatins and reduce overlap, it reduces the number of committees and joint committees from 31 to 28) limits the number of committees and subcommittees on which members may serve folds almost all energy and mineral functions into a single Energy and Natural Resources Committee, and considerably reduces overlapping on environment, transportation and several other functions.

It also gives Republicans a guarantee of roughly one-third staffing on all the committees, to be reached in four years - an objective Republican leaders have been seeking in vain for a generation. Unless it is knocked out on the floor by the Democratic majority, the one-third staffing guarantee alone will probably assure support of the overall reorganization plan by most Republicans.

Stevenson, while conceding that the Rules Committee had hacked out many of his original proposals, said enough remained to make the plan a great improvement over the current system.

"We went for 150 per cent; it looks like we're ending up with 75 per cent," he said, contending that he knew the plan would be cut back so he deliberately wrote one broader than he expected to see approved.

Both Majority Leader Robert C. Byrd (D-WVa.) and Republican Leader Howard H. Baker (Tenn.) expressed support for the Rules Committee resolution and predicted it would clear the Senate. "It's a good package," said Byrd. "Significantly better than what we have now," said Baker.

Key portions of the plan face floor opposition. Chairman Frank Church (D-Idaho) will seek to preserve the Committee on Aging, Chairman George McGovern (D-S.D.) the Nutrition Committee. An attempt to kill the entire reorganization proposal is likely from McGovern or others unhappy with different parts of it. Some Democrats want to kill the one-third GOP staffing guarantee.

In its key features, the plan:

Cuts the number of committees from 31 to 23. Nutrition becomes part of Agriculture, and aging part of Human Resources (now Labor and Public Welfare); Post Office, Civil Service and District of Columbia are folded into Governmental Affairs and the Space Committee into Commerce; Joint Atomic Energy's functions are divided among four committees.

Limits a senator to membership on two of the major standing committees and one "third" committee. The third committees are Rules, Veterans, Intelligence, Small Business, the joint committees and - for certain purposes during the present Congress - Budget and Governmental affairs. The ethics committee, and a new ad hoc committee on Indians, which will expire after this Congress, can be a fourth committee. The original Stevenson plan contemplated that most senators would have only two assignments, but the Rules Committee refused to kill some committees.

Forbids a senator to serve on more than three subcommittees on his major standing committees and two on his "other" committees. In practice this will limit the average senator to eight subcommittees, compared with nearly twice that now, and reduce the number of subcommittees from 174 to perhaps 125. The Appropriations Committee, is exempted from this rule because of the importance and volume of is work.

Limits any senator to one committee chairmanship, and to one subcommittee chairmanship on each committee on which he serves. This will hurt some senior Democrats such as James Eastland (Miss.), who holds three subcommittee chairmanships on the Judiciary Committee which he also heads, and Birch Bayh (Ind.) and Edward M. Kennedy (Mass.), who hold two each on Judiciary. Junior members will get the assignemtns instead.

Provides for a computerized scheduling system and several other mechanisms to reduce overlap on committee meetings.

[WORD ILLEGIBLE] Republicans one-third of all committee staffs within four years, with half the change to be achieved in two. Republicans claim they have only 15 per cent of the staff on Agriculture, 10 per cent on Armed Services, 5 per cent on Foreign Relations, and close to one-third on only three or four committees, although they account for 38 of the 100 senators.

Leaves the Energy and Natural Resources Committee with most of the Interior Committee's existing functions, thus making Chairman Henry M. Jackson (D-Wash.) one of the big winners in the reorganization plan. He keeps minerals and mining, irrigation, lands and parks.

The original Stevenson plan would have killed the committees on Small Business, Veterans and ethics and the Joint Economic and Joint Internal Revenue Taxation committees, among others, reducing the total to 15. But the Rules Committtee kept them alive, under pressure from veterans and small business organizations and powerful Senators seeking to protect their "turf."

In many cases, the Rules Committee blocked Stevenson's plan of rationalizing functions. The Environment and Public Works Committee for example, kept public roads construction and the Banking Committee mass transit, though they were supposed to go to Commerce. Commerce kept oceans, toxic substances and coastal zone management instead of giving them to Environment. Environment kept public buildings. Energy kept irrigation because Northwestern senators who control that committee feared a Southern California raid on Columbia River water if irrigation control were assigned to another committee.

Under the plan as approved by Rules, the following will be the committees:

Agriculture; Appropriations: Armed Services; Banking-Housing-Urban Affairs; Budget; Commerce; Finance; Foreign Relations; Governmental Affairs; Energy and Natural Resources; Environment and Public Works; Judiciary; Human Resources; Rules; Veterans. Small Business; Ethics; Intelligence; Indians; Joint Economic; Joint Internal Revenue; Joint Library; Joint Printing.