All the elements of an Agatha Christie thriller are present: Kidnaping, smuggling, and setranged wife who tried to kill her husband by poisoning his orange juice. And of course a perfect motive - money.

This Uruguayan capital is abuzz with speculation about the grisly murder of one of Uruguay's richest husinessmen last month.

An investigation focusing on the mansions and clubs of Montevideo's leading families, while not resolving the murder, has produced some startling charges against relative of the victim. They are accused of having smuggled out of the country about $100 million in hard currency over the past eight years.

It is unclear whether the currency smuggling was connected with the Sept. 12 murder of Roberto Saenz Gallinal, whose family owns Uruguay's largest tire manufacturing company and several large cattle ranches. His body was cut up and stuffed inside a suitcase found on the outskirts of Montevideo.

At FIRST, it was thought that Saenz's had been a political murder, perpetrated either by the military that runs Uruguay and has a bad interntional reputation for its abuse of human rights - or by terrorist groups.

The once-strong Tupamaros, a leftist urban guerrilla organizations, that-pulled off many terrorist acts here in the early 1970s, were wiped out four years ago after the military ended Uruguay's long tradition of democratic rule. But the Tapamaros have not carried out any known operations recently.

The other possibility was that one of the rightist nationalist groups that do exist here, such as the Azuly Blanco (Blue and White), had turned to murder as a warning to those who want to move the country too quickly back to democratic government.

The problem with these theories, according to a diplomat who has followed the Saenz affair, was that Roberto Saenz had neve been involved in polictics.

After Saenz's body was found, the government promised a full investigation. Montevideo's newspapers, which are heavily censored, published very little after the government announced that its investigation was under way.

The talk around Montevideo's better dinner tables was that Saenz was not killed for political reasons. His murder had the look and feel of a Mafia job, possibly carried out by paid killers sent over from Argentina.

ALTHOUGH THE GOVERNMENT investingation has so far not charged anyone with Roberto Saenz's murder, the investigation did, this past week, lead to other charges that many observers here think provide an adequate explanation for the crime.

The police charged Roberto's brother, Gilberto Saenz Gallinal, his estranged wife, Alicia Garcia de Saenz - a former model the press delights in referring to as la modelo, and eight others with having smuggled $100 million in hard currency out of Uruguay over the past eight years.

According to the information officially released, the smuggling scheme was designed to take advantage of higher interest rates and black markets for dollars in neighboring Argentina and Brazil. This probably meant dealing with some shady gangster types, according to sources who claim to know about these things. Of course, the money was smuggled out in suitcases

In the course of the investigation, the police said they had also discovered that los modelo had recently tried to kill her husband, from whom she is now separated, by poisoning his orange juice.

Although several persons who know Gilberto and Alicia dismissed this as nothing more than a domestic matter which probably had nothing to do with the alleged smuggling operation, it did provide another dollop of gossip for much of the rest of Montevideo. She has not been charged with attempted murder.

Although the proceeding against the Saenzes and their alleged eight accomplices in the smuggling business have not been completed, the authorities have told the newspapers here that the government will seek prison terms for those involved if they are found guilty.

There is still one thing, beyond an official explanation of who killed Roberto, that should provide an interesting end to the Saenz affair: It is not a crime to export currency from Uruguay and nobody can figure out exactly waht law could conceivably have been broken.

The charges against the 10 are "conspiracy to commit a crime," but the crime is not specified. The thinking at the moment is that Gilberto, Alicia and the eight others have, more or less, been accused of committing a "moral crime" against the nation by taking so much money out of the country.

When a visitor asked several well-informed Uruguayans how someone could break a law that was not written down anyplace, he was told it was a good question but that he simply didn't understand the way things work in Uruguay.