The death of Sen. John L. McClellan (D-Ark.) will set off a major shuffle of committee chairmen in the Senate, putting a moderate liberal - Sen. Warren G. Magnuson (D-Wash.) - at the head of the influential Appropriations Committee.

Magnuson was next in line to head appropriations, and has previously said that he would take the job if it fell vacant. Under new Senate rules, he must be elected to the post by the Democratic Caucus, then the full body.

McClellan's passing leaves just four old-line southern committee chairmen in the Senate, and marks another large step in the evolution of that house of Congress away from its traditional image as a club dominated by Southerners.

In fact, McClellan's death may bring noticeable changes pushing the Senate in a more liberal direction. Besides putting Magnuson at the head of the Appropriations Committee, McClellan's death creates a vacancy on the ideologically balanced Senate Judiciary Committee. If the Democratic Causus picks a liberal to fill that position, the entire committee could take on a liberal complexion.

If Magnuson takes over appropriations as is expected. Sen. Howard W. Cannon (D-Nev.) is in line to succeed him as chairman of the Commerce Committee. Such a move by Cannon would in turn create a vacancy at the head of the Rules Committee. Sen. Claiborne Pell (D-R.I.) would be in line to assume that post.

In Arkansas, McClellan's passing will intensify what was already developing as an intense intraparty contest for his Senate seat. McClellan announced last week that he would not seek re-election next year.)

A state law forbids whomever Gov. David Pryor chooses to complete McClellan's term from running for the seat next year, so none of the active candidates for the seat is expected to take the interim appointment.

Pryor himself is expected to run for the Senate seat next year. He unsuccessfully challenged McClellan in a bitter primary fight in 1972.

Other potential candidates include three Democratic House members, Reps. Bill Alexander fo Osceola, Ray Thornton of Sheridan and Jim Guy Tucker Jr. of Little Rock. Tucker was elected last year to succeed Wilbur Mills, who resigned from the House.

State Attorney General Bill Clinton is also regarded as a possible contender.

President Carter yesterday praised McClellan as "a resolute and gifted lawmaker," and said he was "especially grateful for his wise and generous counsel during the early months of my administration."

Senate colleagues began to issue statements on McClellan's death yesterday. Sen. Edward M. Kennedy (D-Mass.), whose later Robert once worked as a special counsel to an investigating committee headed by McClellan, said the Arkansas senator was an example "of the finest American tradition of service of the public."

Majority Leader Robert C. Byrd (D-W.Va.) called the Arkansan "a man of vision, who arthored and guided legislation to make our country a better place to live. In the truest sense of the word, John McClellan was a leader of men," Byrd added.

Sens. Edmund S. Muskie (D-Maine) and jennings Randolph (D-W.Va.) also praised McClellan. More tributes are expected today, when the Senate reconvenes. Most members were still out of the city yesterday.

The only man with more Senate seniority than McClellan at the time of his death was James O. Eastland (D-Miss.), chairman of the Judiciary Committee and one of the four remaining Southern committee chairmen.

The others are Russell B. Long (D-La.), chairman of the Finance Committee, John C. Stennis (D-Miss.), chairman of Armed Services, and Herman E. Talmadge (D-Ga.), chairman of Agriculture.

Gov. Pryor of Arkansas did not indicate yesterday when he would name an interim replacement for McClellan.