NEW JERSEY'S Gov. Brendan T. Byrne called it a "historic moment" and undoubtedly it was. At a table on the boardwalk, he was signing legislation to permit casino gambling in Atlantic City. And at the moment he signed, he ensured that the tattered old resort will never be the same again.

Most of the residents of the place seem to think this brave new world they are entering will be a happy one. They see their ships coming in in the form of new hotels, new visitors, new jobs and lots of money changing hands. They hope to get some of that money - and some of them already have from the property they have sold to those who want to get in on the ground floor of the East Coast's version of Las Vegas. So they were out in force Thursday to welcome in the new era in a manner reminiscent of the old Atlantic City: confetti, bands, balloons, clowns and oratory. There was even a local minister proclaiming in the opening prayer, "We are here to celebrate the birth of new Atlantic City."

Well, we hope their dreams come true. But, to be honest about it, we keep having something more like a nightmare when we think about the new Atlantic City - a nightmare no bigger than the Mob. We can't get out of our head the well-known weakness of organized crime for gambling, legal as well as illegal. Now, we know New Jersey officials say they are taking all the precautions. The legislation permits casinos only in hotels with more than 500 rooms. Those who want casino licenses must have impeccable records. State law-enforcement agencies are being beefed up. And the governor stood there with a stirring message: "Organized crime is not welcome in Atlantic City, and I warn them again to keep your filthy hands out of Atlantic City and keep them the hell out of our state." Strong words, those. But they came from a governor in dire need of help from Atlantic City and just about every place else to get himself even renominated, let alone re-elected. And so we had this sense, as we saw that scene on television, that this was King Canute bading the tide to go no farther. It will be interesting to see if New Jersey can do better.