Gangs of youths wielding knives, iron bars and homemade explosives are roaming many Soviet towns, injuring and killing each other and even challenging police head-on, a newspaper said this week.

In an article chronicling what is emerging as a major social problem across the country, the weekly Literaturnaya Gazeta quoted senior policemen, sociologists and other experts who spoke of a breakdown in public order in many cities."For the last 10 years we have been living a legal lie and this is continuing even in the fourth year of `perestroika' (restucturing)," V.C. Ob-chinski, a senior policeman and academic at an Interior Ministry college said.

"A textbook published this year said that crime has fallen under Soviet rule, especially in the last two decades. In fact, in the last 20 years, teenage crime has doubled."

Soviet experts take as their model Kazan, the capital of the Tartar Autonomous Republic, a city of about 1 million people, around 400 miles east of Moscow, which has become notorious for its gang warfare problems.

According to the article, six youths were killed and 73 hospitalized with serious injuries in 1986-87 after fights in the city involving 900 people armed with knives, clubs and even homemade explosives.

And the problems in the city appear to be growing fast. Another six youths died in fights between rival gangs in the first four months of this year, while gang membership is swelling by 2,000 to 3,000 a year.

However, experts quoted in the article also cited a string of other cities in the Russian Federation, the largest Soviet republic, and in Kazakhstan that they said had also been hit by the gangs.

"Kazan is not a unique phenomenon," one senior law official said.

The gangs mostly group young males ages 14 to18, but children as young as 7 or 8 have come under their influence, the experts charged. Men in their 20s, returning home after military service, have also started joining.

The gangs fight it out among themselves largely over territory. However, the motive is not purely youthful bravado or emotion, the experts said.

Instead, there are also links with lucrative protection rackets particularly focused on schools and colleges where even young children are forced to pay a few kopecks in extortion money.

And behind it all, lies the shadowy figure of organized mafia-style crime, which recent media reports have said is also emerging as a major problem in the Soviet Union.

Soviet experts blame the problem on a breakdown in society caused by a mass exodus from the countryside to the city, coupled with a lack of leisure facilities for young people.