Jeremy Thorpe, the former leader of Britain's Liberal Party, was charged yesterday with conspiring in an unsuccessful attempt to murder a male model, his alleged homosexual lover.

The political scandal, festering here for 16 years, is the biggest since a pair of prostitutes helped bring down a Tory government in 1964. Ironically, this latest could provide a powerful boost to lift the Conservatives back to power.

Thorpe, 49, still a prominent member of Parliament and his party's spokesman on foreign affairs, was charged along with three other men in the magistrate's court at Minehead in West England. His alleged coconspirators are David Holmes, 47, best man at Thorpe's first wedding, godfather to Thorpe's son, and a close friend since their Oxford days: George Deakin, 35, a Welsh businessman who leases pinball machines: and John Le Mesurier, 44, another Welsh entrepreneur who runs a discount carpet store.

The four, who face maximum sentences of life imprisonment, were freed on ball of $5,000 pounds (about $9,650 each). They were ordered to surrender their passports and return for a hearing Sept. 12.

Thorpe announced that he intended to keep his seat in Parliament. A conviction, however, would automatically oust him from Parliament.

At the heart of the scandal is Thorpe's relationship with Norman Scott, 37, a male model who lives in the west of England. Thorpe has steadfastly insisted that he befriended Scott in 1961 out of kindness and never had a sexual relationship with him. Homosexuality betweem consenting adults is not a crime in Britain, but enough public doubt existed to force Thorpe from the Liberals' leadership 2 1/2 years ago. That was not long after he had carried the nation's third party to its greatest postwar electoral showing. When he resigned. Thorpe again denied having a sexual relationship with Scott, but said the publicity and pressure were damaging his effectiveness as a leader.

However, on the eve of his resignation, he gave the press a letter he had sent Scott in 1961. It closed "Yours affectionately, Jeremy, I miss you."

Last October, Andrew Newton, a onetime airline pilot, revived the affair by asserting that a prominent liberal had paid him 5000 pounds to kill Scott.

Newton had just completed a jail sentence for luring Scott to a lonely moor and killing the model's Great Dane.

A key witness against Thorpe could be still another close friend, Peter Bessell. He is a former liberal member of Parliament, now living in Oceanside, Calif.

Bessell helped dislodge Thorpe from his party leadership in 1976 when he told reporters he had paid Scott several pounds a week - perhaps 200 pounds ($385) to 300 pounds ($530) in all - starting in 1967, to protect Thorpe.

Then Holmes, Thorpe's best man and a onetime deputy treasurer of the Liberal Party, acknowledged that he had paid Scott 2,500 pounds ($4,825) on the eve of the February 1974 election. Thorpe's great political achievement. Holmes has said he gave the money for letters that would show Bessell had been paying off Scott. Newspapers already had copies of the damaging letters, but they kept silent.

For his part, Thorpe has repeatedly insisted that he knew nothing of Holmes' payoff. Thorpe, however, has acknowledged that he did ask Bessell to help the jobless Scott.

According to accounts published here. Holmes one of the alleged coconspirators, reportedly met Le Mesurier, the Welsh businessman, and complained that someone was trying to blackmail a friend of his Le Mesurier allegedly introduced Holmes to Deakin, the Welsh painball operator.Deakin has said that he understood Holme's friend merely wanted to scare off the blackmailer.

In October 1975, pilot Newton, an acquaintance of Deakin's arranged to meet Scott at night on the Devon moor. There, Newton shot and killed Scott's dog.

At a subsequent trial, where Newton got two years for possessing a gun with intent to kill, the pilot said Scott had been blackmailing him with a nude photo.

But Newton would change his story when he emerged from jail last fall. Now he claims he had been a hired killer who could not shoot straight because he had been overcome with compassion.

By coincidence, Scott, the supposed victim and blackmailer, was on trial in 1976 at almost the same time as Newton. Scott was accused of defrauding the Social Security Department here. In the course of his testimony, he blurted out:

"I am being hounded . . . just because of may sexual relationship with Jeremy Thorpe."

This time, the press did not ignore the charge and the stage was set for Thorpe's political fall. In fact, Scott had been trying to tell the world of his alleged affair with Thorpe for years. He reportedly first went to the police with it in 1962, a year Thorpe had helped him.

The prosecution case is expected to depend heavily on testimony from Scott, the purported victim-blackmailer: Newton, the alleged hired gun who has not been and Probably cannot be charged with attempted murder; and Thorpe's friend, Bessell if he can be brought from southern California.

In addition, the police are known to have tape recordings of conversations between Newton and the conspirator who allegedly arranged his 5,000 pound payment.

The defense is likely to concentrate on attacking the character and histories of the three prosecution witnesses.

They are in sharp contrast with Thorpe's. The son and grandson of Tory members of Parliament, he attended Eton, Britain's most exclusive private school, the Trinity College at Oxford. At Trinity he met Holmes.

Thorpe was first elected to parliament at 30, in 1959. Seven years later, he became the leader of the dwindling liberal band and then married Caroline Allpass, with whom he had a son in 1969.

A year later, his wife was killed in a car accident and Thorpe sunk into a deep depression. At the 1970 election, the Liberals won only 2.1 million votes and six seats. There was talk of deposing Thorpe.

Eventually, he bounced back and married Marion Stein, a concert pianist who was the Countess of Harewood. In February 1974 he staged a dazzling, personal, American-style campaign and carried the Liberals to 6.1 million votes - 20 percent - and 14 seats.

His party held the balance of power, and Prime Minister Edward Heath offered to make Thorpe foreign minister if he would give the Tories the Liberals' support. Thorpe declined, clearing the way for Harold Wilson and Labor to return.

Eight months later, the Liberals slipped to 5.3 million votes and 13 seats, their present level.

Then came the Scott revelation in court. Bessell's acknowledgement of payments and the Newton claim to have been a hired, if erratic, gun. At the several press conferences where Thorpe has repeatedly proclaimed his innocence, his wife has stood at his side, pale but head high.

Just last fall, after Newton told his latest story, Thorpe issued another statement.

Among other things, he said:

"Not a scrap of evidence has been produced to implicate me in any alleged plot to hire somebody to kill Norman Scott . . . He is neither the only nor the first person I have tried to help. But a close and even affectionate friendship developed from this sympathy. However, no sexual activity of any kind ever took place. Unfortunately, he became too dependent and demanding in terms of attention and I turned to Mr. Bessell, then a close colleague, in the hope that he might be able to help Scott on an impersonal basis . . . I did not know of Mr. David Holmes' negotiations to buy any letters and had I known of these negotiations, I would have stopped them at once . . . I do not know Mr. Newton . . . I have no knowledge of any payment being made to Mr. Newton and know of no arrangement by anyone to pay Mr. Newton."

Thorpe, who was white-faced and under evident stress at Saturday's brief hearing before the magistrates, will now be expected to repeat all this under oath and cross-examination in his fight to keep from prison.

Until Thursday, when Parliament adjourned for the summer, Thorpe regularly attended, spoke frequently and well. Yesterday morning, commentators were saying that his speech on Rhodesia was the best of the Commons' debate.

The political implications of the affair are murky, but any fallout is almost certain to benefit Margaret Thatcher and her Conservatives. Even before yesterday's charges, the Liberals had sunk in the opinion polls here to 6 percents, less than 5 million votes.

A rough rule of thumb suggests that the Liberals take two votes from the Tories for every one from Labor. So any decline in Liberal strength helps Thatcher.

Fears of a collapsing Liberal vote as well as the eclipse of the Scottish nationalists is one more reason why Prime Minister James Callaghan is eager to postpone an election as long as possible. But whether he can put one off beyond October is in doubt.

There is a curious echo in all this. Fifteen years ago, John Profumo, minister of the Army, lied to the House when he denied that he had an affair with Christine Keeler, a call girl. But in a later trial, Keeler and another prostitute, Mandy Rice-Davies, were to testify that the Army minister had shared Keeler's favors with a Soviet naval attache.

That scandal helped tip the scales against the Conservatives the next year, and Harold Wilson narrowly won his first term as a Labor prime minister.