Here is advance notice of a public meeting right out of the Carter era -- a session that will discuss the environmental impact and worker safety of a highly classified, aging, U.S. nuclear weapons building plant; an event that is guaranteed to draw public-interest groups, avid environmentalists, ban-the-bombers and a Soviet agent or two.

In short, it is hardly a program that one would expect to be sponsored by a federal agency under a Reagan administration.

But more than just another agonizing public display of government introspection is involved. There are legitimate federal interests in the safety of workers in dangerous and old government plants and in maintaining a safe environment around them; when these infringe on another federal concern, national security, you have a complex government problem worth exploring.

The facility involved is the Pantex plant in Amarillo, Tex., where every new, nuclear warhead headed for the U.S. stockpile is assembled, and where the old ones are taken apart. It is run by the Department of Energy, which develops and builds the parts for its nuclear bombs, shells and missile warheads at laboratories and plants around the country. But it is at Pantex where they are assembled and then shipped to the military services.

The Pantex plant, which served as a World War II conventional arms depot, has been used to assemble nuclear weapons since 1951. Secrecy was acceptable in those days and it wasn't until 1963 that the plant's function was declassified. The people in Amarillo, 17 miles away, have always hesitated to discuss what went on at the facility and the local papers almost never mentioned it.

That changed somewhat in 1977, when an experimental chemical explosive blew up and killed three workers. Even then, the local people, some 2,000 of whom work at Pantex, accepted the incident without complaint.

But there were legitimate concerns in Washington and elsewhere. Pantex was so old that the eight cells -- areas where the weapons, one-by-one, are assembled by hand -- did not meet federal safety standards.

DOE made extensive, multimillion-dollar plans to modernize the plant, not only to make it safer but also to prepare for the major increase in nuclear warhead production that is under way.

In 1980, a group called the Panhandle Environmental Awareness Committee went into court to demand that DOE provide an environmental impact statement on the new construction at Pantex in compliance with the National Environmental Policy Act. Four years earlier, DOE had studied possible additions to the plant and decided that an impact statement was not required.

Two months ago, DOE reversed its earlier position. The agency, which has completed impact statements on a few of its facilities that build nuclear weapons parts, agreed to put together "a comprehensive analysis" of Pantex's operations, according to a notice in the Apr. 24 Federal Register (page 23285).

On May 28, there will be a "scoping" session in Amarillo, where, for the first time, according to a DOE official, the agency will make a public presentation on the activities at Pantex.

These include according to the Register, "weapons assembly and stockpile surveillance activities" of uranium, plutonium, and tritium, as well as a variety of nonradioactive toxic chemicals."

The impact statement will also address, according to the notice, "DOE-controlled transportation of nuclear weapons components and nuclear weapons into and out of the Pantex plant."

There also will be mention of possible alternatives to Pantex -- relocation of some functions to other locations including Burlington, Iowa, which at one time was the site of nuclear weapon assembly, or the possibilty of transferring the Pantex operation to a new site.

One problem is how far agency is willing to go in discussing the details of the nuclear weapons building operation. Another is that the groups that show up for the May 28 session will not turn it into an antinuclear weapons meeting but rather focus on the issues of environment and safety at Pantex. DOE is asking for advance notice from those who want to speak.

At DOE, the current hope is that the environmental impact statement that emerges in a year or two will end up as an unclassified book with secret appendices that could be read only by those with needed government clearances.

"The unclassified document," a DOE official said recently, "is the only way this exercise will turn out to be of value to the public."