Dublin, Ireland ? The two men drink standing near the back of the long bar at Davy Byrnes, one of the many watering holes in this city that, in the words of writer Samuel Beckett, who once lived upstairs, have been known to house “broken glass and indiscretion.”

In the back, well away from the “whippets” and “blow-ins” who tend to wander in, armed with neither intellect nor wit, if one distinguishes between the two, settle on the first available stool and ask for a “Boodweiser” from the barman.

Standing, because as the long, merry nights wear on, each man must be on his toes, or miss the opportunity to point out a deficiency in the other’s grasp of 13th-century history, or drop a deftly delivered pun, or a magnificent lie.

If there is a common denominator to these long, cantankerous evenings, it is Guinness, the beer so fundamental to Ireland that one has only to say, “Pour me a pint” to receive, in due course, a wide, ceremoniously poured glass of “the black stuff.”

Bitter and muddy, thick with creamy foam, too meaty for the heat but a blessed lubricant for a foggy night and a tearful chorus of “Carrickfergus,” Guinness is Ireland’s best-selling beer. Sixty-somethings like McCutcheon and Winter, weaned on its barley essence as teenagers, wouldn’t even consider drinking a wispy lager in its place.

But even Guinness, it seems, is not immune to the forces of open markets, suburban sprawl and Ireland’s evolution from a backwater of emigrants to one of Europe’s economic powerhouses, a country that imports cheap labor now from Eastern Europe.

Even as sales have boomed elsewhere, Guinness has seen its business decline in Ireland over most of the past seven years, a trend that eased only slightly last year with a growth rate of 3.5 percent.

The problem is, Irish traditions are something many Irish simply no longer have time for.

In Dublin, working and commuting now take up much of the time once spent stopping at the pub for a pint after work. And as the Celtic Tiger begins like everyone else to feel the effects of the global credit crunch, with declining home prices and rising unemployment, it doesn’t help that a pint of Guinness costs $7.20.

“I’ve got a hundred-mile round-trip commute every day. So you’re out of the house for 12, 14 hours a day, and by the time you do get home, all you’re fit for is a couple of hours of TV, maybe dinner, and go to bed. It would never, ever cross my mind to go for a pint on the way home,” said Cormac Billings, a 33-year-old investment banker who works in Dublin’s city center but lives in the suburbs.

Ireland is still the world’s second biggest beer-drinking market, after the Czech Republic. But beer consumption has declined by 15 percent since 2001. Rural pubs last year were closing at the rate of more than one a day, victims of high taxes, increasing supermarket sales and a nationwide smoking ban that went into effect in 2004.

Add to that an explosion in demand for wine and high-end coffee here, and Guinness now sells more beer in Nigeria, with its extra-robust, 7.5 percent alcohol foreign extra stout (“there’s a drop of greatness in every man,” the ads tell Nigeria’s receptive males), than it does on the Emerald Isle.

The company in May announced a $1-billion modernization program that will close two venerable breweries and eliminate more than half of its brewery staff, while transferring most Guinness export production, including beer bound for the U.S., to a new state-of-the-art brewery in the Dublin suburbs.

Pub owners say they still sell more Guinness than anything else, but as Ireland has joined the European Union and become a new center for banking and manufacturing, they face a clientele with more choices and wider interests.

“Years ago, everybody drank Guinness,” said David Donnelly, a 36-year-old Dubliner. “But young people don’t drink Guinness. If I was going for a few drinks with me mates, we just drink Budweiser. Guinness is more of an old fellow’s drink.”