NEW ORLEANS (AP) _ The right cultural mix in an old port city, a winning football team, and the result was linguistically inevitable: ''Who dat say dey gonna beat dem Saints.''

It's a chant that originated at a high school and got attached to the Saints in 1983 by traveling fans in Atlanta during a brief period of euphoria.

The stands - except for the knot of Saints supporters - were quiet. The players could hear it, and they came off the field after the game joining the crowd in the chant: ''Who dat? Who dat? Who dat say dey gonna beat dem Saints?''

A player chorus recorded it over the strains of ''When the Saints Go Marching In,'' but the record died when a series of opponents stepped forward to answer the musical question.

It's back again this year, with the Saints 9-3 and assured of a first-ever playoff berth. On the radio, at games and on the streets of the French Quarter: ''Who dat? Who dat? Who dat say dey gonna beat dem Saints?''

It's the language of this city's blue-collar neighborhoods such as the one in which Saints owner Tom Benson Jr. grew up. Benson, a self-made multimillionaire, still pronounces ''business'' as ''bidness,'' and there's a tendency for ''Oilers'' to come out ''Erlers.''

It's the accent that drew a puzzled glance from President Franklin Roosevelt when then-Mayor Bob Maestri turned to him at a formal dinner and asked him, ''How ya like dem ersters?''

It's also the accent used on the TV series ''Frank's Place'' by actor Don Yesso, a New Orleans native. Yesso's character explained, once, that Frank's Place didn't stock quantities of lobsters because, ''Dey sperl and ya gotta trow dem out.''

Yesso's lines are frequenly interpreted in subtitles.

He's not just acting. He's a legitimate Y'at, as is Benson. ''Y'at'' is a label the Uptown folks pinned on those who used the Downtown greeting, ''Where y'at.''

Actually, ''Where y'at'' is seldom heard anymore. More common is ''How bout dem Saints?''

New Orleans was a fertile linguistic ground for planting a cheer from the black community, where informal speech patterns also include the articles ''dis, dat, dese, dem and dose.''

The Y'at dialect and informal black speech patterns share some characteristic s, said Judy Maxwell, a professor of anthropology at Tulane University.

''Germanic European languages - and some Celtic - don't have the ''th'' sound,'' Maxwell said. ''The standard substitution for that is ''d.''

''You get the same substitution in many black languages. And whether they had the ''th'' sound in their native languages or not, they got it in the pidgin English they were taught as a sort of lingua franca in commerce,'' she said.

So there was no racial or cultural gap to bridge for ''Who dat.'' Y'ats could adopt it as their own with no translation necessary.

As for ''ersters,'' that's part of a change that took place in port cities in America, reflecting changes in the language in England, Maxwell said.

''At the time the changes were happening, we had been separated from England for a long time, but there was still lots of trade,'' she said.

It's no accident that the Y'at dialect in New Orleans was prevalent in the Irish Chanel and the Ninth Ward, both blue-collar riverfront areas where dock workers lived.

''In New York and London, Boston and Charleston, you'll find some similarities,'' Maxwell said.

In New Orleans, a stroll down Bourbon Street in the French Quarter after any Saints game is enough to imprint ''Who dat'' permanently in the memory.

Mayor Sidney Barthelemy, a high school tackle in his youth, proclaimed 1987 to be ''The Year of the New Orleans Saints'' after the Saints locked up the playoff berth.

''We have forever cast aside our 'Ain't' bags, learned the meaning of Mardi Gras in December and taught the rest of the nation to respect New Orleans football,'' he said in his proclamation.

'''Who Dat?' shall be our battle cry through the remaining three games of the regular season and on the playoff road to the Super Bowl,'' he said.

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