PHILADELPHIA -- These are heady days for Sen. Arlen Specter (R-Pa.), the only Republican member of the Senate Judiciary Committee who is not convinced that U.S. Court of Appeals Judge Robert H. Bork should be elevated to the Supreme Court.

He has been in great demand by the television interview programs. His hometown newspaper, The Philadelphia Inquirer, described the Judiciary Committee hearings on Bork's nomination as "Arlen Specter's finest hour." The New York Times said his questioning of Bork was "brilliant."

None of this praise, however, appeared to have made much of an impression on more than 60 members of the College Republicans chapter at the University of Pennsylvania who waited to ambush Specter here Saturday at a meeting of the Republican State Committee. They milled around outside the meeting room debating which of several possible slogans to shout at Specter.

Finally, an hour behind schedule, Specter and his wife, Joan, arrived at the Franklin Plaza Hotel. The students unfurled their signs -- one said, "Don't Be a Dork; Confirm Bork" -- and began to chant in unison:

"We back Bork. We back Bork. We back Bork."

It has been like this for Specter since July 1, when President Reagan nominated Bork to replace retired Justice Lewis F. Powell Jr. He had a preview of the emotions involved at a town meeting in the state shortly after the nomination was announced when two men almost got into a fist fight over the issue.

Specter is the center of attention because he is one of the handful of moderate Republicans in the Senate -- and the only one on the Judiciary Committee -- whose vote for Bork could not be assumed from the start. When the Bork hearings began, GOP strategists rated Specter the most likely of the three swing senators on the committee to oppose Bork.

Just as southern Democrats are watching another undecided committee member, Sen. Howell Heflin (D-Ala.), other moderate Republicans could be influenced by Specter's decision. Both groups are considered vital to the outcome of the confirmation fight.

As an unpredictable moderate from a state with a large majority of registered Democrats, Specter has been through this kind of thing before. In 1985, the issue was the MX missile, which Specter had opposed the previous year.

It was a bruising battle, including White House threats to cut off fund-raising help for Specter's 1986 reelection campaign. In the end, Specter voted for the MX and then announced he would not have Reagan help raise campaign funds for him.

But there has never been anything like the Bork confirmation fight, Specter said. By the end of last week, his office had received more than 50,000 pieces of mail and almost 50,000 telephone calls. This outpouring of public sentiment has been running about 2 to 1 in favor of Bork's confirmation.

Meanwhile, Specter has seen a steady stream of representatives of groups on both sides of the issue, apparently giving no more clues to his thinking in private than he has in public. "He listens to everyone but keeps his own counsel," said Daniel J. McKenna, Specter's press secretary.

Going home to Pennsylvania offers no respite from the pressure. Joan Specter, a two-term Philadelphia city councilwoman who is running for reelection this year, said the level of interest in the Bork nomination is "unbelievable." She said her dentist was listening to the hearings on the radio during her Friday appointment.

"I can't go anyplace without people coming up and saying have Arlen vote for or against," she said.

The pressure comes in many forms. The deluge of mail to Specter's office included a note from Rep. Robert S. Walker (R-Pa.), an outspoken conservative. In it, Walker reminded Specter of a meeting he attended with about 50 conservative religious leaders during his reelection campaign last year. The subject was Reagan's future judicial appointments.

"I think he made a firm promise to the religious conservatives that he would not oppose any of Reagan's nominations on the basis of philosophy," Walker said. "I was in the meeting when he made that pledge."

The religious right, he added, will see a vote against Bork as "a betrayal." Walker wrote the note during the first week of the hearings, when Bork was put through five grueling days of testimony. While other Judiciary Committee Republicans tried to help Bork build a case for confirmation, Specter, a former prosecuting attorney, asked tough, challenging questions.

Specter's questioning of Bork led some to conclude he was preparing to vote against the nomination. But when Bork opponents testified last week, he also challenged many of their assertions.

The role of prosecutor is "second nature" to Specter, said Sen. John Heinz (R-Pa.), his senior colleague.

"I think Arlen thrives on the opportunity to ask people tough questions; I should know," said Heinz, who narrowly defeated Specter in a 1976 GOP primary. He added that he is as undecided on the Bork nomination as is Specter.

Specter demonstrated both his style and his fence-sitting ability during a brief exchange during the hearings last week with Thomas Sowell, the prominent black economist supporting Bork's nomination.

"Answer the question," he snapped at one point, going on to tell Sowell, "I have a real question about how much you know about Judge Bork." But then Specter said that Bork had "articulated positions that may well warrant confirmation."

"I'm not saying yes or no," he quickly added.

He didn't tell the Republican students yes or no either. As they chanted at him, Specter clasped his hands in a prayful position, a stiff smile frozen on his face. When Guy Ciarrocchi, the president of the group, thrust a pro-Bork button into his hand, telling him it was from "those people who elected President Reagan and yourself," Specter replied, "I will hold on to this."

Specter gave the students a shortened version of the speech he delivered later to the state Republican meeting, employing phrases he has used since before the hearings began.

He said Bork, as a Yale Law School professor, had written many opinions that are "at sharp variance with the traditions of American constitutional law." The question was whether these were only examples of "professorial theorizing" or Bork's likely course on the high court, Specter said. He had deliberately maintained an "open mind," he said, because it is important to hear everyone before making a judgment.

As Specter entered the meeting, the speaker was Sen. Gordon J. Humphrey (R-N.H.), representing the presidential campaign of Rep. Jack Kemp (R-N.Y.). Setting off one of several pro-Bork demonstrations during the day, Humphrey, who sits next to Specter at Judiciary Committee meetings, said, "Let's hear from all of those who believe we should vote to confirm Judge Bork."

"I'm hearing you," Specter later told the crowd.

In an interview, Specter said he had not seen Walker's note but that he did not consider his conversation with the religious leaders last year to involve a pledge. They were mostly concerned about abortion, and he has repeatedly said Bork should not be rejected on that or any other single issue, he noted.

"I am not bound on a decision one way or another," he said.

Specter, who has twice met with White House chief of staff Howard H. Baker Jr. to discuss the Bork nomination, also said that the Reagan administration has "modulated" its approach to him, a change in tactics since the MX fight. "They're letting me know how strongly they feel, but not in the way they did in the past," he said.

One reason may be that Specter is less vulnerable to administration pressure than he was in 1985. In a career marked by several political setbacks, he won a resounding reelection victory with 56 percent of the vote in 1986, a bad year for Senate Republicans.

He does not face another campaign until 1992. By then, the next president will also be seeking reelection and Bork could be either a justice of the Supreme Court or an answer in a trivia quiz.

Walker said that to conservative Republicans the Bork nomination is "a Panama Canal type of issue" and that Specter's vote "is something they are going to remember." But others disagreed.

"There is going to be five years and people are going to forget," said Elayne Bruckman, president of the Pennsylvania Young Republicans and a strong Bork supporter.

There was also a clear tone of sympathy and admiration for Specter among the party regulars who attended the weekend meeting here. The chants of the well-dressed, well-bred Ivy League students were good-natured, without a trace of anger. "I don't envy you," one party official told Specter. Another man approached him and said, "I certainly hope you confirm him. I know you'll do the right thing."

Those should be comforting words as Specter approaches a vote he calculates will make roughly half of his 12 million constituents "madder than hell." As they were leaving the meeting, someone asked Joan Specter, "How's it going?"

"I think it's going all right," she said. "We have five more years."