AMSTERDAM - The scene at the 420 Cafe on a recent Friday was typical of what many travelers have come to associate with Amsterdam. Behind the bar, Janne Svensson, 34, weighed out small quantities of marijuana and hashish for her customers, many from foreign countries. They sat quietly, smoking and sipping coffee, as familiar strains of Jimi Hendrix drifted softly from the stereo and giant manta rays cavorted in a nature video on a big-screen television.

While there are many attractions in the Netherlands, nearly a quarter of this city's more than four million foreign tourists a year will visit its coffee shops, where the sale of small quantities of cannabis is tolerated.

But Amsterdam's days as a destination for hazy holidays may be numbered. Prime Minister Mark Rutte's right-wing coalition government is pushing to restrict the operations of the coffee shops and to prohibit the sale of the drugs to nonresidents. The first phase of his plan would begin May 1.

"I think that by the end of next year, there will be no drug tourism in the Netherlands," said Ard van der Steur, a Parliament member and a spokesman for Mr. Rutte's People's Party for Freedom and Democracy. Strictly speaking, the sale of marijuana and hashish is not legal. But a longstanding policy of tolerance means that licensed coffee shop operators are not prosecuted as long as they deal in limited quantities and keep hard drugs and minors out. The Dutch are also allowed to cultivate up to five marijuana plants each for their personal use.

In some respects, tolerance appears to have been successful: despite the easy availability, the Dutch are far less likely than Americans or many other Europeans to use marijuana.

The impetus for changing the policy originated with, of all things, a parking shortage. In the southern city of Maastricht, hundreds of drug tourists drive in daily from elsewhere in Europe to purchase marijuana, creating an infuriating traffic nuisance.

Spotting an opportunity, clandestine dealers have begun offering foreign drivers the option of buying their cannabis without ever leaving their cars. Local residents are unhappy that drugs are back on the streets.

Mr. Rutte's justice minister, Ivo Opstelten, has said that, as of May 1, coffee shops in three southern provinces are to be turned into members-only clubs, limited to 2,000 Dutch clients each. They are to maintain a registry and check IDs. The rest of the country's coffee shops are to follow suit on January 1, 2013.

Mr. van der Steur said that the main problem with the current policy was that marijuana production had led to the creation of an expansive black market. Dutch cannabis exports are thought to be greater than the country's annual flower exports, which are worth $6.6 billion.

"We now function as a supplier of drugs for the rest of Europe," he said.

Mr. van der Steur said the government would begin treating high-potency marijuana as a hard drug, like heroin and cocaine, prohibiting its sale in shops. Growers now breed marijuana that is almost three times stronger than it was a few decades ago, he said. "The product changed totally, but the policy didn't," he said.

Michael Veling, 56, owner of the 420 Cafe, and the spokesman for the Cannabis Retailers Association, said he was skeptical that the government would get its way. More likely, he said, the policy change would be struck down in court, or the issue would be left up to the municipal councils.

But if the law changes, "I'm not going to build a register," he said. "I'm not going to discriminate on the basis of nationality. I've only ever discriminated on the basis of behavior. I'll go back to selling alcohol" - illegal in coffee shops since 1996 - "and go back to selling bags of weed under the counter," as he did before the toleration policy was adopted.

His customers were dubious as well. Kenny and Sean, preppy-looking American college students on a tour of Europe, acknowledged that the availability of marijuana was one reason for their visit.

"If you smoke weed, you have to go to Amsterdam before you die," said Kenny. "This place would die if they changed the weed laws. We know that. We're business students."

The New York Times