They thought they had B'rer Rabbit in the briar patch, but in the end it was the senators who were stuck in the tar.

Bert Lance not only survived that first day in court he had kept saying he wanted, he succeeded in staging another kind of trial. As his artfully crafted defense portrayed things, it wasn't Lance who was on trial; it was the senators, the regulators, the press, the Bill of Rights, the leakers of secret information who stood in the dock.

Lance had not come to the lion's den just to defend himself. He was there fighting for human rights and the System.

"I did not ask for this fight," he said in the glare of the lights, "but now that I am in it, I am fighting not only for myself . . . but also for our system."

And the system, as Lance presents it, comes straight from Horatio Alger: small-town boy makes good, moves onward and upward, and wants to repay his fortune by serving his country.

"I was a successful businessman in my home state," Lance said, stating his recurring theme, "and I thought I had an important contribution to make by coming into government service.

"I have worked hard in these past eight months in Washington, and I am proud of the job I have done in OMB [the Office of Management and Budget] But is it part of our American system that a man can be drummed out of government by a series of false charges, half-truths, misrepresentations, innuendos and the like?"

When Lance strode quietly into that chamber at 9:45 yesterday morning, he already had been consigned to doom. The question in Washington wasn't if he was going; it was when. Maybe even then. A supporter walked up to him, looking uneasy, shook hands, wished him luck and told him consolingly he wasn't alone.

"I don't feel lonely today at all," Lance said jovially.

As events quickly proved, Lance had no need to feel that way. It was the senators who were on the defensive, carping and squabbling among themselves. At one point they fell to debating, with mock-seriousness, just how much the official investigators should be investigated, and by whom.

When Sen. Abraham A. Ribicoff (D. Conn.) finally gaveled the first day into history at 5:12 p.m. it was even possible to think that Lance might survive after all. If so, it could turn into a Pyrrhic victory for the Carter administration. But that remains to be seen.

In opening the session, Ribicoff told Lance: "We don't intend this to be a trial by ordeal." On the first day, at least, the ordeal seemed to be borne more by the senators than the banker-turned -budget director.

It was a day that began with solemnity and tension, and quickly degenerated into political caterwauling.

Not since Watergate had Washington witnessed such a scene, and many of the trappings were familiar: the army of photographers and reporters, the long lines of spectators drawn inevitably to the promised sensation, the glimpses of emotion and character.

At Lance's side through it all was Clark Clifford, the consummate Washington insider, now assisting one of the key Carter outsiders newly come to town from Georgia.

Clifford has been advising Presidents since Lance was a teenager in the hills of north Georgia. If there was any doubt about the fine hand of his counsel in Lance's long, subtly drawn opening statement, all you had to do was look across at the green-felt-covered table where Lance sat forward, alone, in the spotlight. Slightly to his left and behind him, Clifford sat soundlessly repeating the words as Lance uttered them.

Later, Clifford put on and took off pince-nez glasses as he methodically studied the unfolding testimony.

The defense was simple, and initially effective. It was to let Lance quietly go on the attack and act the wounded businessman and public servant.

He came on strong in expressing his outrage about his personal ordeal these past weeks. "My experience has been one of profound shock and disappointment," he said at one point. "The rights that I though I had as an American have been treated in the most irresponsible and destructive manner."

He spoke of smears and premature verdicts of guilt creating "a saddening and disillusioning experience."

Where he had been struck, he said, was where he had lived: "All my adult life I have been a banker. My reputation, in effect, has been my life and my property."

As for the allegations about his business acumen, the overdrafts and the rest, Lance followed a consistent pattern. "I make no apology for this practice," he said in telling how for years the Calhoun bank followed "a liberal policy with respect to overdrafts."

In effect, he was saying, whatever practice he followed was open to all. Everyone could do it. That was the system.

Consistently, he played down the embarrassing practices that have received so much public discussion and scrutiny of late. The question of overdrafts was one of "degree." The sustaining of large overdrafts was "an acceptable practice" in a small, rural bank.

They were all paid off, anyway, and "not one penny was ever charged off as a loss." And whatever loss might have existed was "negligible."

He referred from time to time, with carefully stated precision, to such things as "certain imprudent loans" and a "routine referral of this matter" when discussing a Justice Department investigation of his activities.

But the Bert Lance who was sketched in his own testimony yesterday was just a drawling country banker following the American dream. He was the $90-a-week bank clerk working hard to support his wife. They pooled their resources to buy their first stock in the bank, he said, not mentioning that he married the bank president's daughter. Newssman normally the business, increasing the assets.

And as he progressed, his horizons widened: "My plans for the bank included a program to develop a network of correspondent banking relationships, establish a national account department, conduct an aggressive agri-business program and become involved in international banking."

He had as he said, "an expansion program." Part of that was using the bank's plane for personal trips: he was creating a new image and new business whenever and wherever he traveled.

Lance was an effective witness in his own behalf yesterday - unruffled, in control, at ease. He had said he felt secure and comfortable, and clearly seemed to be.

Not all the members of his personal entourage sitting behind him appeared as calm and confident during the testimony. Some wore stricken, worried looks, and his son's eyes welled with tears as Lance began testifying. But through it all, Lance's wife, LaBelle, sat staring straight ahead, smiling slightly and looking perfectly at peace.

Lance took his case not so much to the senators as to the people. He welcomed them, he said, "as the jury in this proceeding."

How that wverdict will be rendered is unclear despite the disarray of yesterday's opening session, there was more than a hint of harder time ahead for Lance. The questioning, if diffuse, was centering on his personel, as well as professional, dealings.

What's really on trial in Lance's case is more than his reputation. It's a question of public confidence in political office holders. As a measure of how complicated that judgment can be, consider two of the opposing citations yesterday.

A Republican senator William V. Roth, Jr. of delaware, quotes a Democratic public official, Lance, summons a Republican President.

Between them, they defined the larger questions. Roth, question Jimmy Carter as his authority: "There is a simple and effective way for public officials to regain public trust - be trustworthy."

Lance, going back to Abraham Lincoln for his final words: "I do the very best I know how - the very best I can: and I mean to keep doing so until the end."