Hugh B. Kaufman has been a nagging voice from the depths of the Environmental Protection Agency for more than four years. But these days, he is doing his singing from the catbird seat.

Six congressional panels have launched investigations to determine if the agency's hazardous waste program has been manipulated to give "sweetheart" deals to industry or a political edge to the administration's friends. They will start with information Kaufman has provided.

His boss, Rita M. Lavelle, has been fired, along with several top aides, at least partly to avert a charge that she perjured herself by denying she wanted Kaufman fired.

In the last few days, less than a year after the administration called him a "media ham" spouting worthless opinions and faulty data, Kaufman's phone has been ringing nonstop with calls from reporters eager to carry his latest pronouncement.

Last Wednesday he taped a Phil Donahue show that will be seen here this week. And today he intends to tell it to the judge.

In an administrative law hearing being held at EPA's request, Kaufman will attempt to prove that high-level agency officials tried to find embarrassing episodes in his past, loaded him with work to build a case for incompetence and had him followed to a Pennsylvania speaking engagement. He was photographed there, entering and leaving a motel room with a woman--who turned out to be his wife.

An investigation by the Labor Department, which has jurisdiction in EPA employe complaints, found in December that the agency's handling of the matter was "extraordinary" and its explanations "implausible."

But Kaufman says he can prove more, now that EPA has appealed that decision. Armed with dozens of internal documents and the power to put agency officials under oath, he believes he can demonstrate that an endless string of misdeeds, leading to the White House, was committed in an effort to shut him up.

"I can show criminal activities at the behest of the White House or polluters as a method of silencing me," he said in an interview in his lawyer's office last week. White House officials declined to respond to Kaufman's statement.

The 40-year-old toxic waste specialist is on his way to becoming the most celebrated government whistleblower since A. Ernest Fitzgerald, who touched off a long-running controversy in 1969 by disclosing a $2 billion cost overrun on the C5A aircraft. Fitzgerald lost his job as a result, and it took him 13 years to get it back.

Kaufman will be trying to prove that the administration had the same fate in mind for him. But he said it is not his job that is important.

"I don't care whether I'm fired or not," he said. "I've helped raise the public consciousness. I've put my finger in the dike at a time when the civil servants, who I think are just trying to do a good job, were scared to death."

What Kaufman has been telling the media, Congress, citizen's groups and just about anybody else who will listen, is that the dangers of dumped or inadequately stored toxic wastes are not going away, and they are not being significantly reduced.

Not in this administration, not in the last. Not even under the vaunted "Superfund," the $1.6 billion law passed by Congress in 1980 after the Love Canal episode in New York brought the issue to a flashpoint.

He started spreading his message in 1978, first to a congressional subcommittee trying to get a handle on the size of the toxic waste problem. Kaufman, then the chief investigator in the hazardous waste division, contends that he was instructed by Carter administration EPA officials not to find or investigate any more sites. Carter administration officials retaliated by removing him from his job as chief investigator, but they did not kick him out of the agency.

"In the Carter administration, it was much more gentlepersonly," he said. "The general counsel would prepare memos that would try to trap me. I'd write memos back."

In the Reagan administration, Kaufman's attacks got sharper. In speeches to a host of citizen and environmental groups, he contended that EPA officials were not only refusing to exercise their authority to clean up toxic waste dumps, but also were letting companies create new dumps.

Kaufman says EPA officials responded with their own arms escalation. "This administration focused on me as a strategy to put the agency to sleep," he said. "But they went over the line."

Kaufman is hardly without critics, even among those who support what he is doing. His dealings with the press have drawn charges, not all from the administration, that he is a publicity hound and a manipulator. He delivers his assessment of the facts with the kind of blunt certainty that borders on arrogance.

And his view of others, through his ethical prism, makes him an occasional irritant even to environmentalists, who say sometimes it makes sense to compromise.

Some environmental groups squirmed uncomfortably last year when Kaufman turned his shrill whistle on them, saying they had sold out the hazardous waste laws for the sake of clean air.

In the waning days of the lame-duck Congress, a bill to close what environmentalists regarded as a gaping loophole in toxic waste law died in the Senate Environment and Public Works Committee when Chairman Robert T. Stafford (R-Vt.) said there was no time.

Kaufman contends that Stafford killed the bill to fulfill his end of a three-way deal with the White House and national environmental groups, a deal that helped him survive a tough primary fight and a general election battle against an opponent favored by many Vermont environmental groups.

According to Kaufman, Stafford promised the White House he would kill the provision that would close the loophole if the administration would not oppose him in the primary for his support of stronger air pollution laws. To the environmentalists, Stafford promised an unwavering stand on clean air if they would help him withstand charges in Vermont that his environmental record was not as good as his opponent's.

Environmentalists deny that any trades were involved. Ray Post, Stafford's campaign manager, said such a deal was "outside the realm of possibility. It would not be in the style of Stafford to involve himself in that kind of tradeoff."

Whether Kaufman is at the root of the current EPA controversy or not, even his critics give him credit for his tenacity and his motives. "He's not playing politics," said one conservation official. "He cares about the environment. That's what drives him."

That, and perhaps a sense of duty. When he joined EPA 12 years ago, he said, "I signed an oath of office, and it was not to the president. It was to the American people."

He used the same line on the Donahue show. It brought applause.