As scandals go, it has the makings of a classic: a slowly unraveling string of revelations, suspicion of a coverup and a central figure called Nixon.

The opposition in Parlaiment has dubbed it "Slaughtergate."

Other elements of the story include a squabble over states' rights and memories of a longdead race horse. But these aspects are peripheral to the scandal's potential damage to millions of dollars worth of trade and Australia's international image.

The Australian meat export scandal began a month and a half ago, when U.S. officials found horse meat in Australian beef shipped to a San Diego plant that processes meat products for a fast-food restaurant chain. Australian officials then discovered horse and kangaroo meat in boxes of beef bound for the United States from a Melbourne export company.

Under pressure, the Australian government has formed a Royal Commission to investigate the affair, and further revelations about meat substitution in the domestic market are widely expected.

The opposition Labor Party has called for the resignation of the minister responsible for the sector, Peter Nixon, who is making a world tour in an effort to restore foreign confidence in Australia's $1.3 billion-a-year meat export industry.

Critics charge that the government of Prime Minister Malcolm Fraser has tried to contain the scandal at every turn, only to see it lurch out of control.

"The general belief is that the degree of meat substitution is much higher for the domestic market than for the export market," said an Australian who has followed the issue closely.

"I suspect we have been eating a lot of 'roo [kangaroo] meat and not knowing it," said Labor member of Parlaiment John Kerin.

For Australians, the thought of eating kangaroo meat is not quite as disconcerting as it is for Americans. Although not on the menus of most city restaurants, it is commonly eaten in the rough interior region called the Outback and has been a staple in the diets of aborigines for thousands of years.

The aversion here to substituting kangaroo meat for beef stems largely from the way the kangaroos are killed. After being shot by professional kangaroo hunters, they are gutted and the carcasses thrown on trucks. Then the carcases are carried hundreds of miles before the hides are removed.

"In many cases those carcases are in a rotten condition before being processed into pet food, let alone for substitution in beef for the U.S. market," one expert said.

He pointed out that at the same time the beef export scandal was exposed in the United States, an outbreak of salmonella, traced to salami produced by a Melbourne firm, killed one person here and made several others seriously ill.

Although still only a side issue, the scandel has added to pressures on the government from inside and outside the ruling coalition. Political observers see the scandal as contributing to charges of maladministration by the Fraser government and criticism of his coalition partner, the National Country Party. Nixon is a member of the party.

Especially damaging to the Fraser government have been revelations that Nixon knew of allegations about illegal practices in the meat industry for as long as a year before the scandal broke, and that the federal police, Australia's equivalent of the FBI, had been awarea of such charges since 1975.

The issue surfaced in 1977 when it was brought up in Parliament by Sen. Cyril Primmer, a Labor Party member from Victoria, where the current scandal originated. He charged then that meat substitution was taking place, named the firms involved and described how it was being done.

The matter was referred to Ian Sinclair, Nixon's predecessor as minister for primary industry and also a member of the National Country Party. Sinclair later released a brief statement saying that a police investigation showed there was nothing to the allegations.

Government opponents charge that when the scandal finally broke as a result of disclosures in the United States, the Fraser administration compounded it by trying to rein it in.

"The minister [Nixon] wasn't prepared to do anything at first," said Kerin, who is the Labor Party's spokesman on primary industry. "He just didn't seem to take it seriously."

"The resulting publicity and scandal have done us immeasurable harm," another critic said. "We now have the reputation of some third-rate banana republic run by a bunch of hucksters and out to con everybody we can."

The administration first set up a government inderdepartmental committee to look into the scandal. When that was criticized as inadequate, the government turned the matter over to the police to investigate, sent Nixon overseas and finally acceded to opposition demands for a full judicial inquiry by a Royal Commission. Similiar to a U.S. grand jury, the Royal Commission will have the power to subpoena witnesses and conduct a full-scale probe.

According to a government official, the commission may take two months to set up.

Since the opposition called for the commission early last month, the case has taken some new twists.After the acknowledgements that Nixon and the federal police had already known of the allegations, Nixon announced the suspension for 30 days of export operations by all meat processing plants in Victoria State.

At the same time, police in Victoria leaked word that meat exporters in the state had been consistently tipped off about when American officials were to arrive to conduct spot checks of Australian plants processing meat for the United States. Later in the month Nixon announced the discovery of more horsemeat mixed with U.S.-bound beef.

Nixon and other officials of the Ministry for Primary Industry have apparently been trying to play down the scandal, pointing out that the three illegal processors discovered so far accounted for less than 1 percent of the exports to the United States. The United States buys about 60 percent of Australia's total meat exports, amounting to $700 million during the 1980-81 fiscal year, the officials said.

Although Australian newspapers have reported that cattle ranchers and slaughterhouses have been hard hit by the scandal, a senior ministry official, who did not want to be identified, asserted that the affair has had not significant impact on the industry and that the U.S. market had been slow since the beginning of the year anyway.

The government's apparent reluctance to expose the malpractices has been seized by the opposition has been darkly of more sinister motives.

Kerin last month alluded to allegations "including not only fraud on a massive scale, but possible corruption at an offical level and a political coverup to protect supporters of the National Country Party."

So far police have arrested one man in the case, a manager of one of the three Melbourne companies from which all the adulterated beef found up to now had originated.

One reason that the export market has been the focus of attnetion is that Australia has a federal inspection system only for foreign-bound meat. A dispute over state's rights has so far prevented the federal government from extending the system to the domestic market. Inspection of meat consumed in Australia is thus left to the states, and each has its own laws and methods.

Despite the potentially serious impact on the huge Australian meat export industry, some Australians derive a mischievous satisfaction from putting one over on the Americans. This is where the race horse comes in.

It seems that in the 1930s a famous Australian horse named Phar Lap was winning every race in sight here, when it owners decided to go for the big money by taking it to America.

But after winning a big race in California, the mighty gelding, known also as "the Red Terror," suddendly died in the prime of life. Australians were convinced that Phar Lap was poisoned by rival American horse owners. So popular was the horse what a newspaper of the day ran the headline, "Nation Mourns." Phar Lap's heart, weighing about 12 pounds, was enshrined at the Institute of Anatomy in Canberra and its hide hung in a Melbourne museum.

To this day Australians have not forgotten the horse's mysterious death. So the adulterated beef scandal has received another nickname: "Phar Lap's revenge."