In a move that should make Mexico less perilous for American visitors, the Mexican government has decided it will no longer press charges against persons holding small amounts of heroin, cocaine or marijuana that are clearly intended for personal use.

As a result, 15 Americans have already been secretly handed over to U.S. officials and sent across the border in the last two weeks.

Another 30 Americans should be released by the end of this month when the authorities plan to drop charges against some 2,000 persons who have been arrested, but not yet tried, for possessing small quantities of drugs, said Mexico's new attorney general.

The attorney general, Oscar Flores, said in an interview that he is moving to solve another bilateral headache, the problem of aircraft and cars stolen in the United States and brought to Mexico. Owners have charged that Mexico was vioant the 1936 U.S. Mexican convention in return of stolen property.

Of almost 200 stolen U.S. aircraft listed as awaiting release or investigation, only 16 were returned in the last three-years. But in the past month, Mexico has handed over 42 stolen planes to the U.S. embassy for return to their owners.

Officials are now tackling the enormous task of checking thousands of cars to see if they were stolen in the United States. "It looks like the Americans are more interested in collecting their insurance money rather than in collecting their car," said Flores. "People try to get their planes back, but they rarely bother with a car."

The aim of the drugs decision. Flores said, is to reduce the chances that people are subjected to arbitrary arrests and extorlion by police and lawyers when caught with small amounts.

At present, said, Mexico's tought anti-drug laws are lopsided, with too much punishment for the small user. "Even if the person does not get a long sentence, it may take a year for the trial to come up. And in that time, dishonest police and lawyers have often had a chance to bleed people for money."

Every year, almost 3 million American tourists come to Mexico. Many more cross the border for short trips. As marijuana smoking spread in the United States, the number of Americans caught here with the coveted "Mexican gold" increased. The 15 persons released this month, for example, were all arrested with only a few marijuana cigarettes and held for three to four months.

A treaty, permitting Mexicans and Americans arrested across the border to serve their sentences at home, awaits ratification and enabling legislation.

The unexpected Mexican policy change toward small drug users does not apply to traffickers. Of the Americans currently held in Mexican jails at least half have been accused of transporting cocaine from south America or dealing in large amounts of Mexican marijuana or heroin destined for sale in the United States.

"We are not changing the law and not establishing any minimum amount permitted," the attorney general warned. "We'll look at everything case by case. Somebody with only five cigarettes caught selling at a school is a pusher, as far as I'm concerned."

A tough, outspoken and pragmatic man, Flores has brought considerable relief to U.S. embassy officials here who found it difficult to deal with the often antagonistic previous administration.

"I'll give you your prisoners, if you just move them out of the country immediately, the same day," Flores told U.S. consular officials.

"Sure we'll take them," U.S. Consul General Vernon McAninch replied. For the 15 newly released Americans, the U.S. consolate hastily raised money from the prisoners' friends or relatives or made loans for the return tickets. "Of course we are very pleased with this new development," McAninch said.