For most members of Congress, ascending to the lofty perch of chairman or ranking minority member of a major committee means power, prestige and perquisties. For Sen. Henry Bellmon (R-Olka.), the honors have included hanging in effigy from a neighbor's porch back home in Red Rock, Okla.

A plain-spoken, round-faced, barrel-chested rancher who came to the Senate 11 years ago with little more than a reputation for having made Republicanism respectatable in Oklahoma, Bellmon struck many of his colleagues as a perfect specimen of predictable and rock-solid Western conservatism.

"Maybe even a hick," said one of them.

Few if any had immediate cause to expect Bellmon would emerge as one of the Senate's most thoughtful and independent members, often rowing against the tide of his party, his constituency and his own political philosophy to hold the line on defense and farm spending, resist tax cuts and even support deficit spending at times.

But that is what has happened.

Now that Bellmon has decided to go back to Red Rock next year at the end of his second term, saying simply that "12 years is enough," his impending departure is being mourned by Democrats as much as Republicans.

"It's going to be a real loss," said Senate Budget Committee Chairman Edmund S. Muskie (D-Maine), who, together with Bellmon as ranking minority member, fashioned the Senate's latest experiment with budget control into an exercise in bipartisan self-discipline.

Some even say the process, as it was shaped jointly by the generally conservative, easy-going Bellmon and the more liberal, volatile Muskie, may not survive the breakup of this senatorial "odd couple" act.

It was as the senior Republican on the Budget Committee over the last four years that Bellmon's reputation as a prairie statesman began to emerge, even though friends say it was more a case of rising to a challenge than any basic change in the man.

"I think it was a case of [unrecognized] qualities being given a chance to express themselves, said Muskie, describing Bellmon as a "true moderate . . . with a lot of common sense."

The 58-year-old Oklahoman has charted a distinctly independent course on other matters as well, voting consistently against anti-school-busing resolutions and supporting the Panama Canal treaties -- to the dismay, and in some outrage, of his conservative constituents and colleagues.

But it was for his budget-inspired resistance to demands of the American Agriculture Movement for huge subsidies that Henry Bellmon had to look at Henry Bellmon hanging in effigy every time he went back to Red Rock. And it is in his budget role that he has made his mark on the Senate.

Bellmon's unusual role arose not so much from law, tradition or political conniving as did it from the almost accidental convergence of two people who, despite glaring differences in temperament and outlook, shared a common background.

Republican Bellmon, like Democrat Muskie, helped build his party in his native state from next to nothing. Each was elected governor when his party was still a tiny minority and had to rely on bipartisan cooperation to get anything done.

So the move toward accomodation was almost second nature when they confronted each other in the recently formed Budget Committee in 1975. They decided then to aim for consensus in committee and to stand together on the floor to defend the compromise budget resolution -- under which Congress sets spending priorities and limits -- from assaults by either left or right.

Time and again, this has brought Bellmon to his feet to oppose GOP efforts to fatten the defense budget; even though he considers himself a strong defense advocate, just as Muskie arises to oppose expansion of domestic social programs that he favors. And it was found Bellmon opposing tax cuts and fixed taxing limits, despite the fact he joined the committee to help carry out his belief in spending restraints and balanced budgets.

Natural as the cooperation may have seemed to them, the House, operating with a different cast of characters and different scenario of pressures, has taken the opposite approach. House Republicans have generally let the Democratic majority write the budget and then opposed it, although some of them say they would cooperate more if the Democrats would let them.

Bellmon's approach is not without its critcs. Some, such as Sen. Orrin Hatch (R-Utah), contend that the GOP should be more aggresive in pushing for a balanced budget rather than, as he puts it, "condoning deficit spending." fEven some of Bellmon's admirers say he could fight a little harder.

As the former governor of a no-deficit state, Bellmon acknowledges that his views have changed since joining the Budget Committee.

"I probably came here with an overly simplistic approach to federal financing due to my experience in the governor's office and due to my conviction that government budgets ought to be balanced every year," he said in a recent interview.

"Here we have two responsibilities that states don't have: for national defense and economic stability. As I've gotten into this thing, I've come to appreciate those additional responsibilities and to accept the fact that there are good reasons for occasional unbalancing of the federal budget," added Bellmon, although he made it clear he wants to see the budget balanced this year even though he will also press for an increase in defense spending.

As for those who prefer the more aggressive partisanship of the House Republicans, he notes that the Senate's version of the budget has nearly always provided for higher defense outlays, lower domestic outlays and less spending in general than the House version.

As for Muskie, Bellmon says "he's a real prince."

Difficult as some of his fiscal votes may have been, he probably took the greatest heat for his support of the Panama Canal treaties. Newspaper editorials back home called him a "traitor," which is tough for a former Marine like Bellmon to take.

Acknowledging it was a tough decision, he said a colleague gave him a book on Panama's history, which led him to the conclusion that the old treaty was "just not equitable to Panama." Moreover, he concluded that Congress was not prepared to support a "mean, costly and distasteful" military campaign to retain the canal. Besides, he said simply, "We don't stay where we aren't wanted."

Reared by parents who came from Iowa and Kansas and brought up in an area of north-central Oklahoma where the local minority was Indian rather than black, he came by his pro-civil rights votes much more easily.

Although Oklahoma City had been into turmoil by a court-mandated busing order, "I became convinced we had to integrate and that local school boards couldn't handle it alone. There was a role for the federal courts. Otherwise we were headed down the road to civil strife," he explained. For reasons he still doesn't understand but deeply appreciates, Oklahoma City reelected him by a bigger margin after his busing votes than before.

Bellmon professes no further political ambition and plans to return to his 3,000-acre wheat and cattle farm near Red Rock. He acknowledges he was tempted to stay on longer but, paraphrasing former senator John Pastore (D-R.I.), said he thought it was better to leave while friends urged you to stay than to stay so long that friends urged you to leave.

"It's sad to see people here so long they have no home to go back to," said Bellmon. "When it comes to the point where we belong here rather than there, we've stayed too long."