Jeremy Thorpe, the dapper wit who once held the balance of political power in Britain, today was ordered to stand trial for allegedly plotting the bungled murder of his supposed male lover.

Three lay magistrates in the West England resort town of Minehead held that the state has presented a strong enough case to try the fallen Liberal Party leader and three other men.

So, the most lured political scandal here in years is to go before judge and jury at the famous Old Bailey Court, probably in the early spring.

In Minehead today, Thorpe firmly told the magistrates, "I plead not guilty and I will vigorously defend this matter."

Thorpe,49, still a member of Parliament and a privy councillor to the queen, appeared at ease, chatting with friends, reporters and his wife Marion, an Austrian-born concert pianist who has been at his side throughout the long ordeal.

Less than five years ago, then prime minister Edward Heath pleaded with Thorpe to form a coalition that would have kept Harold Wilson and the Labor Party from power. Thorpe, who had led the Liberals from near extinction to their greatest electoral triumph in half a century, proudly declined.

Now he must fight against a conviction that could put him in jail for the rest of his life.

For the past three weeks, Britons have been titillated by graphic accounts of supposed lovemaking between Thorpe and the alleged target of the plot, Norman Scott, by tales of a $10,000 payoff to an amateur "hit man," and by stories of large payments by the press and foreign television to key prosecution witnesses.

The only matter held back has been Scott's clinical description of his preparation and response on the night, 17 years ago, when he claims Thorpe first seduced him.

The Minehead "committal" proceeding bears only a remote relationship to the secret sessions of a grand jury that indict accused persons in the United States. The three magistrates are untrained in the law, and the Minehead bench consisted of an architect, a farmer and a housewife.

They can close their hearings only if all defendants agree. But one of the accused coconspirators with Thorpe, the man who allegedly hired Scott's would-be-killer, insisted that the prosecution case be reported in full.

The prosecution charges Thorpe on two counts: conspiring with three others to do away with Scott and inciting Robert Holmes, his close friend since their days at Trinity College, Oxford, to arrange the murder.

According to the state, Thorpe befriended and seduced Scott, a stable hand and then a male model, in the early 1960s. Thorpe, it is said, feared that exposure of the affair would ruin a brilliant political career that began when he was elected to the House of Commons in 1959.

In the state's version, Thorpe repeatedly spoke of the importance of removing Scott with Peter Bessell, 57, a former friend, ex-Liberal member of Parliament and the prosection's key witness.

Holmes, 48, best man at Thorpe's first wedding, a one-time Liberal Party treasurer and now an investment banker was supposedly brought in on the scheme. On the eve of the February 1974 election, Thorpe's great triumph, Holmes allegedly paid Scott $5,000 for his letters from Thorpe. This, too was bungled. They had been copied and were circulating in Fleet Street for several years.

Holmes is said to have found John Le Mesurier, 46, a South Wales discount carpet dealer and another defendant in the alleged conspiracy. Le Mesurier in turn led Holmes to George Deakin, 38, a South Wales night club and slot machine operator, according to the state's version.

Deakin, the fourth and last man charged with conspiracy, allegedly hired Andrew Newton, 32, to kill Scott.

Newton testified that in October 1975 he lured the model to a lonely Devonshire moor, shot and killed his Great Dane Rinka, but drew back from firing at Scott himeself.

Newton was then sentenced for two years for having a firearm with intent to do bodily harm. He now says he perjured himself at this trial where he said nothing of Thorpe and claimed Scott was blackmailing him.

By chance, at almost the same time, Scott was on trial for defrauding the Social Security Administration. There, in open court, he blurted out that he was being persecuted because of his affair with Thorpe. The various charges then began to emerge in the press.

When Newton came out of jail in 1977, he says that Le Mesurier, the carpet man, gave him about $10,000 dollars for the murder he failed to pull off.

The Minehead hearing was devoted entirely to the stat's case and the defense cross-examination of the prosecution witnesses, so no detailed Thorpe defense will be disclosed until the trial itself.

But a statement Thorpe supposedly gave police last summer was read out and in it he strongly denied everything. He vigorously denied any homosexual relationship with Scott and said he had simply befriended a sick young man from "compassion and kindness." He strenuously denied plotting Scott's death or any knowledge of a payoff to Newton.

The closet thing to an admission of wrongdoing came from lawyers for Deakin, the club owner, and Holmes, Thorpe's friend. The lawyers said that both had at worst plotted to frighten off Scott, not kill him.

From the cross-examination it appears that Thorpe's defense will be directed largely at attacking the character of the state's major witnesses-Bessell, Thorpe's old friend who fled to Mexico and the United States after rolling up business debts estimated at $700,000; Newton, the dog killer, and Scott.

Under examination, all three were forced to admit that they have repeatedly lied.Bessell was told:

"You don't know when you are telling the truth and when you are telling lies."

"I accept that as a problem," Bessell answered.

All three also acknowledged that they stand to profit from convictions by selling their "memoirs" to press and television. Under British libel law, they would have trouble making law, they would have trouble making another pound if Thorpe is acquitted.

Perhaps the most astonishing feature of the case so far is Thorpe's public composure. His outward manner is the same as it was when he starred in parliamentary debates or compaigned in gleeful high spirits in 1974. He wears the same elegant Edwardian clothes, sports a gold watch chain and makes small jokes.

Even if Thorpe is acquitted, he is almost certainly a ruined man, a stunning fall for a politician who once briefly could dream of occupying Number 10 Downing Street. CAPTION: Picture, Jeremy Thorpe arrives at a recent hearing befor magistrates who yesterday ruled he must be tried on a murder conspiracy charge. UPI