The territorial instinct in the U.S. Senate is very powerful. For the moment, a burning issue for the Senate establishment is where to find the office space for Sen. Hubert H. Humphrey (D-Minn.) to which he is entitled under a special resolution naming him Senate Deputy President Pro Tem.

The Senate approved the package of special benefits for humphrey as a mark of respect for the man who was Vice President from 1965 to 1969 and was Democratic candidate in the 1968 presidential race - and also as a consolation price after Sen. Robert C. Byrd (D-W.Va.) won the majority leader post coveted by Humphrey. The benefits include a chauffeured limousine, a $52,000 salary instead of $44,600, a suit of extra offices, the new title, and the right to hire several extra staffers for the extra offices.

Humphrey wants the additional office space to be in the Capitol Building, not one of the outlying Senate office buildings. he wants room enough to hold receptions and to house staff. That means a suite of at least two spacious rooms.

Most of the good offices in the Senate wing of the Capitol are spoken for Byrd, immediately after his election as majority leader, moved into the three-room suite long held by the previous Majority Leader, Mike Mansfield (D-Mont.), who had retired. It is a few steps from the Senate chambers on the second floor.

Republican leader Howard H. Baker (B-Tenn.), for his part, immediately took possession of the fine suite not far from Byrd's which had been vacated by the retiring GOP leader, Hugh Scott (R-Pa.).

Meanwhile, the new Democratic assistant leader, Alan Cranston (D-Calif.), headed for the big, beautiful three-roomer used by Byrd when he had the assistant leader job. This is really the nicest leadership office but on the first floor rear, a bit remote from the chamber. The smaller GOP assistant leader office on the second floor of the Capitol building went to the new assistant GOP leader, Ted Stevens (R-Alaska).

Where to put Humphrey? One suggestion is to give him a section of the Senate Democratic Policy Committee staff office on the third floor and move its inhabitants to one of the out-lying buildings. Another. Give him the two-room suite on the third floor used by the Secretary to the Democratic Majority (though it is too small for receptions). A third: Throw the Senate barber shop out of its first-floor space in the Capitol and rebuild it for Humphrey.

These great matters are now being pondered by some of the Senate's finest minds and a decision will ultimately be made by the Senate Rules Committee and leadership.