Rayburn D. Hanzlik's job is to collect the excess money some oil companies charged for gasoline, heating oil and other petroleum products during more than seven years of government price controls. He is now trying to persuade the nation that the amount he is supposed to collect is nowhere near $10 billion to $20 billion.

Those oft-repeated figures, he said in an interview, are "grossly inflated." The General Accounting Office's estimate of $13 billion is also "grossly inflated," he said. Overcharges probably were about 15 percent of those figures (about $1.5 billion to $3 billion), he estimated, and, he said, his agency is developing better numbers.

The 43-year-old veteran of previous administrations is now chief of the Energy Department's Economic Regulatory Administration. He came back to Washington this time from a Los Angeles law firm, where he was a legal adviser to an Alaska oil refinery project. Although he has been in Washington for only three months, he has created some problems for himself on Capitol Hill.

Besides calling the overcharge figures inflated, he announced a reorganization of his office that includes cutting field offices from 50 to eight and reducing personnel by 150, and was quoted as telling Oklahoma City Republicans that the law he is supposed to enforce is "a monster the courts would no doubt throw out."

Hanzlik's goal is to put his agency out of business by Sept. 30, and that is the crux of the problem. When petroleum price and allocation controls were lifted by President Reagan early last year, Congress demanded and received assurances from Energy Secretary James B. Edwards that there would be "no amnesty" for violators.

Funds were appropriated to keep the Economic Regulatory Administration operating until the overcharge cases were either settled or referred to the Justice Department for litigation.

Hanzlik's controversial characterization of the Emergency Petroleum Allocation Act of 1973 was reported in the Oklahoma City Times, along with comments that appear to suggest that oil companies would be better off litigating overcharge accusations than settling them, as some have done.

"We'll actually work a higher figure through out-of-court settlements than you might get in court," Hanzlik said, according to The Times. "But litigation would be preferable because we believe most of these laws and regulations would be thrown out in court. From an academic standpoint, it would be good to show how irrational and how flimsy most of this act was."

In an interview with The Washington Post, Hanzlik said, "I would never phrase it that way," but the reporter "may have it on a tape machine. I certainly wouldn't state that as a policy."

"What I was trying to say," he told The Post, "and this is what I believe: we have 1,000 pending cases we have to clean up. The reason most of these cases are still here is because this is a new law, never litigated, and our folks have had to make some interpretive calls. It's my experience so far that we have on a number of cases made too liberal an interpretation of the law."

The Oklahoma City Times story prompted Rep. John D. Dingell (D-Mich.), chairman of the the House Energy and Commerce oversight subcommittee, to ask the Energy Department's inspector general for a full investigation. Dingell also suggested Hanzlik resign, which Hanzlik said he has no intention of doing. "I have to explain to Dingell that his concern has no basis."

But don't the administrator's comments encourage, even invite, the oil companies to balk at out-of-court settlements and to litigate forever?

Hanzlik said he doesn't think so. Nonetheless, he said, "If I am faced with a law where I think I will have a tough time in court, I will try to settle it. Litigation takes a long time, and there is a possibility I will lose. The oil companies agree with this approach becasuse they don't know how the litigation is going to come out. From their standpoint, it is equally attractive to get it off their books and go on with their business."

It will be particularly attractive if the companies end up owing only 15 percent of the original estimates. Hanzlik conceded he has a public relations problem explaining that one.

"It's very complicated," he said. He said an auditor would go into an oil refinery, find a month-long overcharge at one of 100 points in the system, infer from that that the overcharge occurred over a lengthy period of time, and compute a large figure.

After the company was served with a notice of probable violation and permitted to present more evidence, Hanzlik said, he has learned that auditors frequently had discovered aberrations or shifts in funds that "washed out" in subsequent transactions long before the petroleum product was sold to a middleman or even at the gasoline pump. No damage, no penalty.

That does not mean, Hanzlik said, that there were no overcharges.

"We've got some bad guys out there," he said. "People have taken advantage of the system and those are the ones we particularly want to identify."