AS HE CLEARED out his desk last week, ending 36 years as administrative assistant to retired Sen. James O. Eastland (D-Miss.), Courtney Pace came across correspondence bearing the signature of his boss.

Staring at the scrawled name, Pace grainned and said, "I've forget Jim Eastland's name so many times I can't tell my copy from the real thing."

Pace and Eastland, both 74, are going home to Mississippi after working together as senator and chief aide longer than any other team in the history of the U.S. Senate.

Their personal and professional relationship began in 1927, when, as fledgling lawyers, they were elected to the Mississippi House of Representatives. (Another freshman legislator that year was John C. Stennis, who, with Eastland's retirement, became Mississippi's senior senator.)

Since the two men first came to Washington in 1941 (Eastland served 88 days of an unexpired term before winning the first of his six full terms in 1942), it's not only their handwriting that has become identical.

"I don't recall a single thing on which we differed," Pace mused.

"I could tell how he'd vote on every issue," Pace said, admitting that sometimes he told callers how Eastland would vote on upcoming legislation and then would forget to tell the boss about it. "But he never let me down," Pace said.

Eastland explained his decision to ask Pace to come to Washington with him simply: "He was my best friend. He was scrupulously honest. That's why he's had my complete trust."

Pace and Eastland served only one term in the legislature, and then, because of the Depression, tried to eke out a living practicing law in nearby towns.

Except for that short period, during which they saw each other almost daily and "shared some fees together," they have worked together for half a century.

As befits that long a partnership, they are the picture of two men totally at ease with each other.

Eastland could yell, "Be quiet Courtney, I can't hear!" when Pace's wheezing -- the result of smoking 60 Pall Malls a day -- was so loud it made it difficult talking on the telephone.

And Pace, the alter ego, could shoot back, "Jim Eastland was first elected by his daddy. We were both elected by our daddies. We were 23-year-old kids and we ran on their names."

During their one term in the Mississippi legislature (1928-32), Reps. Pace and Eastland "fought the power structure" and generally sided with the minority within the state's one-party system.

But in the years that followed, "both of us became very conservative," Pace said recently as he and Eastland reminisced about their careers.

Pace ndded in the direction of the owl-faced man who served as chairman of the Senate Judiciary Committee longer than anyone. "You know," he said, "when I first met Jim Eastland, he was a flaming liberal. He's a reactionary now."

Eastland flipped the butt of a burning cigar in the direction of a waste basket and drawled, "I spose so, Courtney."

Later, Pace was asked if he ever wished that it would have worked out so that he were the senator and Eastland the aide.

"Nope," he said, matter-of-factly. "I didn't make it, but neither did 200 million others."

In his more than 3 1/2 decades on the Hill, Pace attended nine inaugurals, dealt with the administrations of eight presidents -- "Truman, Nixon and Johnson all called me by my first name" -- and helped persuade Eisenhower to make a speech in Vicksburg that led to that staunchly Confederate town's first observance of Independence Day.

The changes Pace has witnessed have been "almost indescribable."

The size and salaries of the staffs have mushroomed. Initially, Pace was one of four employes. He and another co-secretary were paid $3,600 (the term administrative assistant did not come along until 1948), compared to his final salary of $49,941. Two stenographers were paid $2,000 each. Last year, two dozen Eastland staffers were paid more than $525,000. The Senator's own salary has gone from $10,000 to $57,500.

In the early years, Pace and other chief aides could stroll onto the Senate floor at will; he recalled once sitting on the steps in the House gallery, near the speaker's podium, to hear a presidential address. Now, except in rare instances when staffers are working on specific legislation, aides are barred from the floor.

Pace hasn't encountered "one thing monotonous about this job. Every person who comes in the door has a different problem."

Incidentially, when Pace first arrived on the Hill, he felt intimidated by the doors to Senate offices, which were always closed. So he tacked up a "walk in" sign on Eastland's door, and now all 100 Senators have some kind of a welcoming message posted.

"Barry Goldwater has his in four languages -- Hipi, Navajo, Spanish and English," Pace said with a touch of pride.

Although he and Eastland have become more conservative, they kept up with some social change. Eastland had two blacks on his staff during his last term, and the last time Eastland ran, Pace noted, the boss welcomed and got an endorsement from the Mississippi chapter of the NAACP.

The close relationship between Pace and Eastland extended to their sons. Casey Pace and Woods Eastland both attended St. Stephen's School in Alexandria, where the young Pace succeeded the senator's son as student body president. On the football field, Eastland-to-Pace was St. Stephen's quarterback-to-end passing combination.

Like their fathers, the younger men have maintained their friendship as adults. Woods Eastland, 34, manages the Eastland plantation, and Casey Pace, 33, lives in Jackson and advises the Mississippi state government on federal revenue sharing programs.

The elder Pace could have tetired years ago, but there was never any question that "if Jim Eastland had sought reelection, I'd be staying. But he's going, and I'm going."

Although he retained the title of AA, in recent years Pace said he was "what you might call emeritus."

He could often be found resting on a long leather couch, equipped with two bed pillows for afternoon naps, instead of at his desk, which like his fingers, was stained from his three-pack-a-day consumptin of non-filter cigarettes.

"People who wanted access to the chairman came to me," said Pace. The day-to-day functions of the office were directed by two younger men, Sam A. Thompson and William G. Simpson.

Pace wasn't the only long-time employe in Eastland's suite. Jean Allen, the senator's personal secretary, worked there 33 years; Frances Chaplain, his casework secretary, 32 years; and Pace's own secretary, Vivian Dubielle, 22 years.

Pace's wife, Charlotte, whom he met in Jackson when he was a freshman legislator, died in 1965. Since then, he has lived alone, the last nine years in a small apartment two blocks from the Capitol.

He was "never much of a socialite" and in the last few years found himself "more and more out-of-step" at cocktail parties, especially because "I forfeited my right to drink long ago."

His only recreation has been reading.

"I've read every damned western in the Library of Congress," he bragged. He devoured four or five novels a week, maintaining his interest by "developing a fine-tuned defective memory. I can read a western one week and a month later reread it and it will be as bright as a new copyright."

Although he spent half of his 74 years in Washington, Pace contends that he never caught Potpmac Fever.

"I'm a Mississippian," he said, savoring the drawl. His roots are all "back home," as are his son, daughter-in-law and two grandchildren.

He has rented a two-bedroom apartment in Jackson in anticipation of "a sunset of babysitting." There also will be frequent trips to the Eastland plantation, 150 miles away near Cleveland, Miss.

Even if he didn't have a family back home, Pace would leave Washington.

"My friends are all gone. If I want to see them, I have to go to the graveyard," he said as he packed the final cartons in his office this week.

"It's sad, but without my Hill contacts, I'd have nothing here," Pace concluded. "My whole life has revolved around this office."