In this year of embattled Republican governors, Pennsylvania's Richard L. Thornburgh sticks out like a well thumb.

In Maryland, New York and most of New England, Republicans are struggling uphill to win Democratic state capitols. West of here, in Ohio, Michigan, Illinois, Wisconsin, Iowa and Minnesota, Republican incumbents have either bailed out or are struggling hard for survival.

But Thornburgh, 50, is apparently coasting to a second four-year term over Rep. Allen E. Ertel, the three-term congressman from this area, who is still trying, just a month before the election, to get his name pronounced right by introducers and interviewers. (The emphasis is on the first syllable, not the second.)

The Pennsylvania Poll in the Pittsburgh Post-Gazette on Friday showed Thornburgh leading Ertel by 56 percent to 33 percent, despite double-digit unemployment in this old industrial state, which contains 600,000 more registered Democrats than Republicans.

When asked why Thornburgh is likely to save his head when, all about him, other Republican governors are losing theirs, political observers here point to Three Mile Island. The accident that shut down the nuclear power plant there in April, 1979, was a calamity to the utility company and the nuclear power industry. But it gave Thornburgh, who had been in office just 72 days, a showcase for leadership that few politicians ever enjoy.

With public uncertainty about the danger verging on panic, Thornburgh drew widespread praise for striking the necessary note of calm and control. When President Carter visited the state, he praised Thornburgh for "a superlative job."

Thornburgh's role in the crisis is so well-remembered that he is not even using it in his campaign television ads. "We've got a spot on it, but it's being held in reserve," said Jay Waldman, his special counsel and political strategist. "It's strong stuff and we may not even need it."

Instead, the governor's television ads highlight other factors that underlie his strength, according to opinion polls.

Coming in on the heels of a scandal-ridden Democratic administration, Thornburgh has dealt summarily with chicanery in state government and made it squeaky clean by Harrisburg standards. A former U.S. attorney in Pittsburgh and assistant attorney general in the Ford administration, he has sponsored a state anti-crime program that includes mandatory minimum sentences and expansion of jail facilities.

Unlike his Democratic predecessor, Milton Shapp, Thornburgh got all four of his budgets through the legislature on time. He is the first governor in more than 30 years to avoid a sales or income tax increase.

Thornburgh also claims credit for improving the business climate in the state and boosting education and human service programs in a time of fiscal austerity. Those claims are subject to dispute and have now been obscured by the recession, which has crippled the steel industry and pushed unemployment in Pennsylvania to 10.6 percent.

The Democratic Party here, since Shapp's defeat, has been singularly lacking in money, leadership and muscle. Thornburgh is outspending Ertel by about 4 to 1, not counting the resources of his office.

But the root of Thornburgh's strength was best expressed by a veteran Republican political operative. "He's probably the best governor in my lifetime," this middle-aged man said, even though he added that he did not like Thornburgh personally.

In a mass-media age of charisma politics, Thornburgh is described by friend and foe as a wooden public speaker who generates little electricity in a room and conveys little warmth on television. He is surrounded, they say, by a tightly knit circle suspicious of outsiders.

"There is a dark underside to Dick's personality," said a fellow Republican officeholder. "He can be mean and vindictive. When you're around him, you sense there's still a lot of prosecutor in his makeup. I'm surprised his personality defects haven't hurt him politically, but they haven't. He's been very skillful politically."

That skill showed in 1978, when Thornburgh maneuvered through a crowded Republican primary field for nomination, then overcame a big early lead of the Democratic nominee, former Pittsburgh Mayor Pete Flaherty, to win by 228,000 votes. He put together an exceptionally strong cabinet, raiding business and academia for both Republicans and Democrats to fill key jobs.

"When I first came to Harrisburg, I was an outsider," Thornburgh said in a recent interview, "and worse than that, a prosecutor who put some of their friends in jail."

He also had defeated the Republican leaders of the state House and state Senate in the primary. For the first two years of his term, Democrats controlled half the legislature. Even after 1980, GOP margins were razor-thin.

But Thornburgh learned to work well with his party's legislative leadership and suffered few setbacks.

"I started out not prepared to like him," said Republican House Speaker Matthew Ryan, who had backed another candidate for the nomination. "But my first impression was that he was a no-nonsense guy, who had his program well in mind, and we better get on the bandwagon, 'cause that's the direction he was going."

For all Ertel's problems, few think that Thornburgh can count on a landslide. Ertel contends that his private polls show him only 12 points back, and with a major registration effort, he believes he can overcome that deficit.

He blames Thornburgh for rising utility rates, higher property taxes and for being "a do-nothing governor" in a time of economic crisis. The revived state AFL-CIO is backing Ertel, and the Pennsylvania State Education Association is laboring to beat Thornburgh with the fury of a jilted lover.

"Remember in November," says the banner on its building across from the state capitol, referring to Thornburgh's "promise" of 50 percent state funding of basic elementary school costs. State funding actually has declined to 39 percent, but Thornburgh denies he broke any pledge.

After remaining neutral in the 1980 presidential primary, to the chagrin of old Rockefeller allies who backed George Bush, Thornburgh strongly endorsed President Reagan's budget and tax cuts. Even now, when many industrial-state Republicans are putting distance between themselves and those policies, Thornburgh says, "It's no time to push the panic button. These policies deserve a chance to work."

Republican National Committeewoman Elsie Hillman, an old friend from Pittsburgh and the Rockefeller days, thinks Thornburgh's conversion to Reaganomics is sincere. "I think he changed when he became governor, and faced those budget and tax issues himself," she said.

Others see a long-term calculation by Thornburgh: a spot on the 1984 ticket if Reagan does not run again, or if he does and wins, an appointment to an administration job when his gubernatorial term expires in 1986.

However, Sen. John Heinz, his fellow Republican, also has national ambitions and is expected to run even more strongly than Thornburgh in his reelection race against Allegheny County Commissioner Cyril Wecht. The prospect of playing second fiddle to Heinz galls Thornburgh, Republican officials say. Last spring, the two feuded openly about who would get the more prominent place -- and the biggest financial share -- from a Reagan fund-raising visit.

Heinz is not the only prominent Republican feuding with Thornburgh. Sen. Arlen Specter, who was defeated by Thornburgh in the 1978 gubernatorial primary and opposed by Thornburgh's candidate in the 1980 senatorial primary, reportedly is suspicious that Thornburgh may seek his seat in 1986. Lt. Gov. William W. Scranton (R), namesake son of a former governor and presumed favorite to succeed Thornburgh, has complained of being "frozen out" by the governor's inner circle.