The war on drugs, President Reagan has proclaimed, "is an untold American success story," and the use of illegal drugs, he said, "has already gone out of style in the United States."

But as the White House Conference for a Drug Free America convenes here today, critics of the Reagan administration's efforts to fight drug abuse say there is a large element of wishful thinking in Reagan's pronouncement.

On the two major fronts where the drug war has been waged -- cutting supply and reducing demand -- experts say they see something less than victory. They see slight signs of progress -- at least among the middle class -- on the demand side, but virtually none on supply.

"I don't think we've turned the corner on keeping illegal drugs out of the country," said Lois Haight Herrington, chairman of the White House conference, "but we've stopped losing the battle for the American mind."

"If we didn't have Nancy Reagan we wouldn't have anything," said Rep. Charles B. Rangel (D-N.Y.), chairman of the Select Committee on Narcotics Abuse and Control. "Advances in stopping drugs -- we haven't made any," he said.

Of the $21.54 billion spent on combatting drugs during the Reagan administration, according to the Office of Management and Budget, the $16.5 billion poured into the effort to cut the supply has had little effect on the current drug of choice, cocaine.

Use is up, inventories are high, prices are down, and the cocaine sold on the street has never been purer, according to the National Narcotics Intelligence Consumers Committee Report and other sources.

"There is greater awareness of the drug problem, and that is good," said Sen. Dennis DeConcini (D-Ariz.), "but the interdiction program is only beginning to pay off with big hits."

Efforts to eradicate cocaine at the source, it is universally agreed, have failed. The Coast Guard, Customs Service, Drug Enforcement Administration (DEA), Immigration and Naturalization Service, Navy, Air Force, Federal Bureau of Investigation, and others have together been unable to eliminate cocaine smuggling on sea or land. State and local law enforcement officials are swamped.

Shortly before the president announced in Mexico on Feb. 18 that drugs had gone out of style, a senior administration official briefing reporters at the White House about the trip said, "If you measure by the flow of drugs {from Mexico}, and that really is the bottom line . . . the flow of drugs is increasing . . . 31 metric tons of cocaine consumed in the U.S. in 1982 . . . 72 metric tons in 1985."

"We're not winning the war on cocaine," said Coast Guard Adm. Paul Yost, and officials of the DEA and Customs Service would agree.

For Reagan, demand has always been the bottom line -- taking the "customers away from the drugs," as he put it in his first presidential news conference. He recently cited surveys showing that the use of cocaine by high school seniors dropped for the first time last year; that drug use in the military has dropped by 67 percent, and that more Americans appear to have absorbed Nancy Reagan's message that drug use is dirty, dangerous and addictive.

He is far from alone in seeing such signs of progress.

"There has been a profound change in attitudes about drugs," said Robert DuPont, head of the National Institute on Drug Abuse under President Jimmy Carter. "Every single trend is going in the right direction." But, he added, "The epidemic is very much with us right now and likely to be with us for another decade -- a lot of time for the recruitment of new victims with new tragedies.

"My question is, there has been a tremendous increase in expenditures for law enforcement, and what has been the return on investment?"

The drug supply side is a difficult question to almost everyone involved.

The problem, according to Yost, is not that money has been wasted on a failed interdiction effort, but that not enough resources have been committed to succeed.

"My friend the Customs commissioner said that every 150 pounds of cocaine causes one death," said Yost. "If it is anywhere near that, every 150 pounds of cocaine I interdict, I save somebody's life."

But according to Yost, more than half of the Coast Guard drug fleet is currently sitting idle at the dock. The men and women staffing these vessels and airplanes are "twiddling their thumbs."

The reason, he said, is the equivalent of the missing horseshoe nail that caused the loss of the war in the old English maxim.

"I need a horseshoe nail," he said, "and the horseshoe nail is $60 million" to send out the drug patrols. That money is tied up in the battle over spending priorities between the White House and Congress.

The military has lent the drug war 12 helicopters, four Hawkeye surveillance airplanes, four surface searching planes, a host of chase planes and other sophisticated surveillance equipment, according to DeConcini, a Senate leader with Sen. Alfonse D'Amato (R-N.Y.) in the effort to cut off drugs at the source.

But Yost points out that the eight new planes designated for the Coast Guard in an 1986 anti-drug abuse act have not arrived. The two Hawkeye surveillance planes assigned to the Coast Guard from the Navy have both been "down for a considerable amount of time," with one up and the "other due up today."

A joint command, control, communications and intelligence center called C I being built on Coast Guard land with Customs Service money will not be ready for another six months.

Of the 16 frigates the Navy is planning to decommission as part of its cost-cutting efforts, eight have been heavily involved in drug interdiction.

Reagan has boasted that in 1981, one country and two states were eradicating narcotics plants, while today 20 countries and 46 states are doing so.

But Tim Carlsgaard, who has traveled extensively on behalf of DeConcini on the antidrug effort, says the promising use of chemicals to kill cocaine plants has been blocked.

Even where foreign governments have cooperated, he said, the problems are not easy to address and the resources few.

Jamaica has committed "a battalion" of the Jamaican defense force to the eradication effort, Carlsgaard said. As a result, where drugs were once grown in 12- to 20-acre plots, fields have now been divided into inaccessible 1 1/2-acre plots.

"Commercial bean plants are growing next to the marijuana plants, and if you wipe out the marijuana, you would wipe out the legitimate crops and the jungle. "Naturally the government says 'no way' to aerial spraying."

Diplomatic efforts to curb international drug traffic have also been troubled. Recently, links between Colombian drug traffickers and officials in Panama, Honduras, the Bahamas, Haiti and Cuba have been alleged in Senate testimony, and Gen. Manuel Antonio Noriega, the military strongman of Panama, was indicted in Florida on drug-related charges.

Mexico has taken more than 2 1/2 years to bring to trial more than 60 individuals accused of the torture-murder of U.S. narcotics officer Enrique Camarena Salazar in 1985. And although seizures of cocaine at the borders have increased since 1981, the National Institute on Drug Abuse estimates that the consumption of cocaine has more than doubled since Reagan took office.

Meanwhile, local law enforcement officials complain bitterly of the administration's failure to fund local law enforcement programs started under the 1986 drug abuse act. The administration says the states have been slow to spend the money they already have.