Sen. Dennis DeConcini's metamorphosis displayed in last week's hearings suggests Judge Robert Bork may be losing his confirmation struggle not because his managers are playing the game badly but because they have been playing the wrong game.

Before the August recess, DeConcini -- a pro-law-and-order, anti-abortion Democrat from Arizona -- seemed a sure vote for confirmation. He returned a different man, as was shown in hostile questioning of Bork. He is a question mark at best.

The explanation is massive pressure against Bork by Democratic constituency groups. Labor, feminists and particularly blacks make clear to senators they will suffer if they vote for Bork. No countervailing sanctions are posed by his advocates.

In the most exhaustive interrogation ever of a Supreme Court nominee's philosophy, Bork, after a shaky first afternoon, performed with patience, wit and erudition. He fulfilled his reputation as a legal intellect and once or twice flashed his celebrated wit. Nevertheless, as he left the witness stand, pessimism prevailed among his supporters.

That is because learned legal discussion at the hearings was largely sham. Senators were seeking not Bork's views but a legal gloss to cover political opposition. The same senators who worried whether Bork's mind was closed now complained he changes it too often.

By not seeking a gloss, Sen. Edward Kennedy displayed candor of sorts. His declaration that Bork regards blacks and women as ''second-class citizens'' was contrary to the facts and offensive even to some Democrats, but mirrored pressure-group propaganda.

So did the assertion by Sen. Paul Simon that the Dred Scott decision, which by protecting slavery mandated the American Civil War, ''reads an awful lot like Robert Bork . . . saying we can't read into the Constitution what is not there.'' Keeping his temper, the ex-law school professor explained to nonlawyer Simon that the decision actually used the Constitution's due process clause (ushering in judicial activism). Disavowing an ideological test, Simon told us last year he would vote to confirm Bork for the Supreme Court. But that was before Simon had entered the race for president and the anti-Bork power play had begun.

The low point at the hearings came when Sen. Patrick Leahy beganharassing Bork for not volunteering to represent the poor without fees. Sen. Gordon Humphrey pointed out the judge had spent 28 years in public service, forgoing millions of dollars in income. An obviously angry Leahy responded that Bork commanded six-figure incomes in consulting fees during three years at Yale. Humphrey pointed out that Bork, now fighting back tears, then faced massive medical bills. His first wife was dying of cancer.

Foreseeing such conduct, conservatives at the Justice Department and White House two months ago proposed a counterstrategy: build a popular Bork constituency based on anticrime policy; energize conservative activists; impose political penalties on senators voting against him. The White House said no.

Instead, strategy was laid out by Washington lobbyist Tom Korologos, a veteran Senate insider who has guided many Republican nominees to confirmation. A conciliatory tone was stressed, and Bork's courtesy calls on senators were mostly upbeat. After his visit with DeConcini, the Arizonan was listed a tentative yes.

DeConcini's post-Labor Day metamorphosis is rooted in political reality. Any threat to him for reelection next year is less likely to come from the divided Arizona Republican Party than from liberal Democrats, who resent his 1986 vote to confirm William Rehnquist as chief justice. Such moderate Democrats are reminded that Florida's Sen. Richard Stone was chewed up by the left in a 1980 Democratic primary.

DeConcini is not the only changed Democrat. Outside the Judiciary Committee, freshman Sen. Richard Shelby of Alabama had been listed for Bork. He returned after Labor Day saying he was not sure and told us he is undecided. Shelby is a conservative Democrat, but his narrow election last year depended on blacks, schoolteachers and union members -- members of organized groups mobilized against Bork.

Unless an 11th-hour counteroffensive is launched by the White House, an ominous line may be drawn. Liberal lobbies will have established that nobody can become a Supreme Court justice without meeting their specifications. That would be an ironic legacy for Ronald Reagan to hand his successors.