In a city where demonstrations come and go as a matter of course, one of the nation's most powerful institutions had long been spared the attention of a protest.

No one had ever bothered to picket the Federal Reserve, at least no one that anyone can remember. It just wasn't one of those demonstration-site favorites, probably because few people understand what really goes on at the Fed. It all seems so technical, so arcane.

But the farmers had been almost everywhere else in Washington since they rolled in more than a month ago. They had lobbied boldly on Capitol Hill. They had tangled fearlessly with the police. And the time came yesterday to face off against the bank regulators.

Rolling along Constitution Avenue, close to the front of yesterday's Last Tractorcade, farmer Tommy Kersey of Unabilla, Ga., finally caught sight of the Federal Reserve building he was bound for.

"Look at all that marble," he said to a reporter with him, awed by the solid mass and alabaster hue of the headquarters of the nation's central bank. "I wonder where they get it all."

From the windows behind the marbled walls, eyes peered back in mutual wonderment. For the normally sober and demure Fed crowd, the coming of the farmers was the most exciting event since Arthur Burns stepped down as chairman of the board.

A small group of aides and secretaries stood on the Fed's front steps and applauded the farm representatives when they strode up. inside, senior officials waited nervously and with some degree of confusion over why they had been singled out for the farmers' last Washington hurrah.

The farmers had a definite purpose in mind. They were mad about high interest rates, just as mad in fact as they were about low grain prices, which was pretty mad.

They wanted a general lowering of interest rates. They also wanted the rates on loans to farmers lowered a little more than the rest. The result would be a two-tier federal discount rate system.

The farmers had been hoping to present their case directly to board Chairman G. William Miller or to any of the other four Fed governors. But the board members, they were told, had a prearranged meeting to attend.

Seven farmers and a lawyer sympathetic to the farmers' cause were suhered into a conference room to meet with four Fed officials. It was easy to tell the two sides apart. The farmers wore jeans, flannel shirts, caps and protest buttons. The bank regulators wore suits.

But the dress code approach could be a bit misleading. There were two pin-striped suits in the room -- one belonged to a Fed official, the other to the farmers' lawyer friend.

It was a testy meeting. The farmers sought to pin much of the blame for inflation on the Fed's high discount rates. Fed officials maintained the riseiscount rate lagged behind the rise in commercial bank rates.

For the most part, though, the bank regulators were determined to avoid a confrontation. They listened as the farmers did most of the talking.

"We feel the policy of the Fed has put a burden not only on agriculture but on the nation as a whole," said farmer Bud Bitner of Walsh, Colo. High interest rates, he added, were strangling the economy.

Not true, said Peter Keir, a Fed specialist, in one of the few instances someone from the bank spoke up. High interest rates are a result of inflation, not a cause of it, he said, and were necessary to squeeze inflationary pressures out of the economy.

"(The low interest rates) you're suggesting would add credit to the economy and would fuel inflation," he told the farmers. "It would also require special regulation to make sure the reduced-interest loans were actually being used for productive purposes."

In the end, board secretary Ted Allison promised the farmers their proposal for a two-tier rate structure would be studied. Afterwards, though, Fed officials said privately the proposal stands little chance of action. "Can you imagine what Congress would say?" said one official. "It's credit allocation. If we give lower rates to one, everyone would want them."

The farmers left the Fed peacefully but saying their venture into the banking world had been a disappointment. They had asked some questions, they said, but hadn't received many answers. The same had been true on Capitol Hill.

They would be driving their tractors out of Washington, they said, with the same sense of despair they had come with -- a despair that takes in not only the future of the small, independent farmer but encompasses the whole, inflation-prone U.S. economic system as well.

"I thought we could come and just present the facts and they'd agree with us here," Kersey said. "Boy was I naive. I've learned you can't play a basketball game in a football field. Next time, we'll just have to define our game better."