Will Thornburgh's experience make him more than a caretaker? A NEW ATTORNEY GENERAL

Richard Thornburgh had been governor of Pennsylvania 72 days when he was confronted with the worst nuclear accident in United States history. But as panic quickened in the spring of 1979 after the accident at Three Mile Island, he moved swiftly to bring calm to the state. Today, it appears that Mr. Thornburgh is being tapped again for his management, his experience, and his calm under pressure. President Reagan announced yesterday his nomination of Thornburgh to replace Edwin Meese III as attorney general and, according to congressional and other sources, he is a shoo-in.

The choice of Thornburgh, though a disappointment to some conservatives who view him as too middle-of-the-road, has both short-run and long-run appeal to the administration, Justice Department watchers say.

In the short run, one department source says, ``we have some legislative matters that need guidance.'' Among them, he says, is legislation that would give government attorneys greater prosecutorial tools; drug legislation; and judicial nominees. In the long run, Thornburgh may be test-driving the position for a longer stint in a possible Bush administration.

Over the last year, as attention focused on Mr. Meese's personal problems, many conservatives noticed that the department's relations with Congress had grown strained, and blamed Meese in part for the legislative slowdown. In particular, they saw the chance to fill federal judgeships with conservative judges slipping away.

Louis Cordia at the conservative Heritage Foundation hopes Thornburgh will pour oil on the troubled congressional waters. With 32 names before the Senate, confirming those judicial nominations would be the most important contribution he could make, he says. But others, like Daniel Popeo, general counsel at the conservative Washington Legal Foundation, say it's too late for anyone, no matter how appealing to Congress, to push judicial nominations through.

Mr. Popeo adds, however, that ``it would be a mistake to view the attorney generalship as a caretaker position.'' The Justice Department, he notes, is ``the biggest law firm in the world,'' and the daily decisions whether to prosecute a case or not, whether to allow mergers to go through, and how to interpret regulations ``is one big job.''

In this, Thornburgh appears to be a good choice. He knows his way around Justice, having served as head of the criminal division in the late 1970s. He set up the Public Integrity section while there - the section that launched the preliminary investigation into Meese's finances. Public Integrity then recommended that Meese be included as a target of an ongoing independent counsel investigation. Last week, the independent counsel decided not to recommend that Meese be indicted for criminal wrongdoing.

If Thornburgh is confirmed, he will also make a mark in the way the administration handles some important Supreme Court cases next term. As attorney general, he would work with Solicitor General Charles Fried on the department's stance on several cases that the Supreme Court is likely to revisit. These cases involve abortion, school prayer, and capital punishment for people who commit crimes when they are under 18.

Thornburgh will have his hands full with the massive probe into the Pentagon procurement process; the biggest-ever investigation into the savings-and-loan industry in the South; high-profile narcotics trafficking cases, such as the possible indictment of Bahamian Prime Minister Lynden Pindling; and white-collar crime cases, including the expected indictment of the investment bank Drexel Burnham Lambert.