Two species of South Pacific lizards currently on display at Washington's National Zoological Park are among the subjects of a two-year federal investigation into the smuggling of rare reptiles, according to sources close to the prosecution.

Three green tree monitors, which are the color of spring leaves and about two feet long, and two Fiji iguanas, which have dinosaur-like heads and gimlet orange eyes are on view in the zoo's reptile house.

The investigation, by a grand jury in Philadelphia, is said to involve hundreds of thousands of dollars worth of exotic reptiles, a number of America's best-known zoos and many big-name animal dealers. A government source said 20 to 35 indictments are expected in two or three weeks.

Edward H. Kohn, deputy director of the National Zoo here, said yesterday that his institution "would want to participate in any thorough investigation." He added, however, "that in light of the current status of the litigation it would be inappropriate to discuss the details" of how the zoo acquired its green tree monitors and Fiji iguanas.

Kohn said he was aware that the federal investigation was under way, but he said he had not been aware of any of the species involved until reading an account of the probe in yesterday's Washington Post.

The green tree monitors, which are found in New Guinea and small islands in the Torres Straits, are said to be worth about $500 each in the wholesale wild animal trade. Fiji iguanas, which come from the Fiji and Tonga islands, are valued at about $600 a pair.

According to investigators, the reptiles were taken illegally in the countries of their origin and imported into the United States in violation of the Lacey Act, which prohibits interstate transportation of illegally taken wildlife.

According to Dr. F. Wayne King, director of zoology and conservation at the New York Zoological Society, there is a thriving international trade in illegally killed or captured animals.

In a chapter he has prepared for a book entitled "Wildlife in America," which is scheduled for publication this summer by the Council on Environmental Quality, King wrote:

"Officials in the Fish and Wildlife Law Enforcement Office in Washington believe that the Lacey Act prohibitions on importing wildlife that was killed or export illegally from the country of origin are virtually unenforceable."

A telephone call to the Fish and Wildlife Enforcement office at 4:25 p.m. yesterday was answered by a record message saying, "No one is in the office at present. At the tone please leave your message and your call will be returned in the morning."

King added, "It is not always easy to establish the legality of exported wildlife. Legal export permits for protected species can often be bought surreptitiously from government officials in the country of origin.

"Holland is the hub of the live animal trade in Europe," he said, adding that some of it is "illegal trade." He said that "Miami dealers count for 93 per cent of all reptile imports" into the United States.

King also wrote that "the vast majority of live animals traded internationally are destined to be sold as pets to private citizens," not to zoos or breeders.

Other reptiles involved in the smuggling investigation include the green tree python, Mackloth's python, the Fiji boa constrictor, Papuan monitor lizards and Johnson's crocodiles.