MOSCOW (AP) _ Moscow Circus director Yuri Nikulin recently threatened to let his lions, tigers and bears loose in the streets unless he received more feed from the government.

After he sent an official request to President Mikhail S. Gorbachev, he got what he wanted.

But for most animal keepers in the Soviet Union, petitioning the president is not an option. In a country where many people cannot find adequate housing and have poor diets, conditions for zoo and circus animals are among the worst in the world.

And the animals' situation has worsened amid the growing chaos in the Soviet economy.

A supplier recently failed to deliver hay to the Moscow Zoo for two consecutive days, and a hungry elephant went on a rampage. One person was injured.

''You can't really make an elephant understand why he's not getting fed,'' said animal trainer Vadim Proshin. ''They don't get it. Instead, they look for someone to blame.''

The situation is just as grim at the Moscow Menagerie, a traveling animal show that has set up shop in the Lenin Hills.

''I feel sorry for the animals living in such conditions,'' said Lyuba Smernova, who took her daughter to see them. ''Those poor bears don't even have room to turn around. Think what will happen to them when the weather gets warmer.''

The exhibit features 85 wild beasts and birds crammed into 10 gaily painted wagons. The animals are either retired or on leave from the circus.

In a fenced-off, 10-by-10 portion of one wagon, a polar bear gazed at visitors. The painted blue-and-white glaciers and snow-capped mountains on the back wall of his cage were smeared with excrement.

Conditions aren't much better at the 127-year-old Moscow Zoo. One employee, Sergei Aliskerov, said that if his country had an animal-protection association, ''probably all the zoos in the Soviet Union would be closed down.''

Since the zoo opened in 1864, authorities have made only one addition, the so-called ''new territory'' built in 1926.

Apart from the construction of an occasional new barrier, some cages have been used since the 19th century, said Aliskerov.

''Three times our bears have bitten off the fingers of people who tried to feed them through the bars,'' said Aliskerov.

The same lethargic bureaucracy that has hampered reforms throughout the Soviet Union are hindering improvements at the zoo.

Workers began building new cages for leopards and tigers three years ago, but they still have not been finished due to numerous snags.

As the large cats languish in tiny antiquated cages, new ones have been vacant for months while zoo officials wait for the workers to complete the final task: welding on the doors.