In a small office above the Kiev International Deli out in deepest Brooklyn, Michael R. Long may hold the political fate of Mayor Rudolph W. Giuliani in his hands.

Long is chairman of the small but powerful New York State Conservative Party, and Giuliani is the presumptive Republican candidate for Senate. No Republican has won statewide election here since 1974 without the Conservative endorsement, and Long is daring Giuliani to try.

All last week, rhetoric flew between the two camps. Long told reporters he was tired of waiting for Giuliani to seek the endorsement. In an interview in his Bay Ridge office, Long warned he has two or three other "bona fide conservatives" who he might run against Hillary Rodham Clinton in place of Giuliani.

Then Texas Gov. George W. Bush, the Republican presidential front-runner, said publicly this week in Austin with Giuliani at his side that he hoped Long's party would endorse Giuliani.

Long called Bush strategist Karl Rove. "Instead of talking to me about supporting Rudy Giuliani, [Bush] ought to sit down with Rudy Giuliani and explain to him about partial-birth abortion . . . about evolving his position," Long recalled telling Rove.

Whether Long or Giuliani will blink first is the latest episode in the theater that is New York politics. In either case, the New York City mayor appears to have a problem other than Clinton's formidable run.

The power of small swing parties like the Conservatives to influence a race, along with a flammable combination of Republican-Conservative personalities and old grudge-mates turned new allies, has suddenly catapulted the Republican Senate campaign into the realm of the unknown.

Will Giuliani make a pilgrimage across the Brooklyn Bridge and kiss Long's ruby ring?

Or will Republican Gov. George Pataki once again run interference for his old enemy, Giuliani, by prevailing on Long to accept Giuliani and his ties to the New York Liberal Party and his stand on abortion?

"What I think Giuliani is waiting for is George W. to put pressure on Pataki to put pressure on Mike to go along with this," one bipartisan political consultant said.

"My understanding is that Giuliani just doesn't want to come across the bridge and lower himself to talk to Mike," the consultant said. But the reality Giuliani faces if he wants to gain up to 300,000 Conservative Party votes, he said, is that the mayor has "got to go across the bridge. He's got to make a move."

Until it's all sorted out, Giuliani's campaign has gone into locked-lip mode. "My on-the-record comment would be: 'I have no comment,' " said Bruce Teitelbaum, Giuliani's exploratory campaign spokesman.

Long said he has received "signals that this is getting out of control, can I cool it." He added that "it's not too late," that the differences aren't irreconcilable.

Bush, who also wants Conservative Party support and met with Long back in October, hopes the mayor will meet with the Conservative Party. "He expects that when Giuliani does that and makes his case to the Conservative Party then they will see he is the right candidate to support," Scott McClellan, a Bush spokesman, said on Friday.

Two weeks ago, it was Democrats who were in chaos--up in arms about the shape of Clinton's campaign and whether she was capable of running, even committed to it. But with her announcement that she's in, her stinging issues-based attack this week on Giuliani's policies on the city's homeless, followed by her announcement on Friday of a campaign manager, she has put all doubt to rest.

Now it's the other side that's gripped with mystery. Not only has Giuliani still not said he is definitely running, but now he's also not signaling how he'll play the Conservative factor.

Its importance to the Republicans is clear. Though Conservative Party members number only about 172,000, they and other small parties can swing New York elections because of unique state rules that allow them to run candidates and for those candidates to run on other party lines. George Pataki became governor in 1994 with both the Republican and Conservative party lines. The Conservatives pulled in 328,000 votes, which turned out to be near Pataki's margin of victory to turn Democrat Mario Cuomo out of office.

To get the Conservative endorsement, Long said, Giuliani must support a ban on partial-birth or late-term abortions and must cut his ties to the small Liberal Party, which helped get him elected mayor.

Giuliani's opposition to the late-term abortion ban is well-known, and Teitelbaum, in televised comments early in the week, said there had been no change. And as for the Liberals, Giuliani is close friends with Liberal President Ray Harding and would have to jettison a friend to satisfy the Conservative demand.

The Conservatives are known generally for having staunch views that are rarely negotiable, said Kieran Mahony, a GOP political consultant whose father once was a Conservative leader. "I would tend to view [their demands] as carved in stone," she said.

The trouble that the GOP faces, though, is stated plainly by Long: "If we run our own candidate, yes, it increases the chances of Hillary winning."

He would not identify the mystery candidates who he said he could field in the race. They do not include, he said, Rep. Rick Lazio (R), who pulled out of the race at Pataki's urging to make way for Giuliani.

The Long-Giuliani face-off over the endorsement goes back to an evening in March.

"It was a very nice evening," Long recalled. "We went to dinner. We talked about nothing for about an hour. I said to him, 'Mr. Mayor, I'm assuming we came here because you are contemplating a run for the U.S. Senate?' "

Long recalled Giuliani being undecided at that time, but Long laid out for him what the Conservatives would require in exchange for their endorsement. He ended by telling the mayor, "If they are too difficult to climb over, just tell me so, because I am inflexible on it."

Giuliani, Long said, did not respond negatively or positively, so Long assumed "we were gonna have negotiations."

They next spoke, but by phone, in August, a day after Pataki's surprise move to push Lazio aside in favor of Giuliani. The mayor expressed his surprise at the move, Long said, but still did not discuss the Conservative endorsement, saying only that he would be in touch.

Since then, Long said, he has heard nothing from Giuliani. He chalked it up to the ambivalence he sees around Giuliani's political positions in general: the Cuomo support, the "running all over the city with Bill Clinton on the crime bill."

"One is suspicious," Long said, raising his eyebrows. "He's not a movement conservative" of the Ronald Reagan mold. "Never was."