A Bulgarian helped two Soviet cosmonauts guide their capsule toward a docking with the Soviet space station Mir and prepared for the busiest program of experiments of any Soviet space flight involving a foreigner.

Alexander Alexandrov, a 36-year-old cosmonaut from the Bulgarian town of Omurtag, will help the Soviets perform more than 40 medical, metallurgical, astronomical and geological studies on Mir, the Russian word for "peace."Friday's schedule calls for the crew to conduct vision experiments in the weightlessness of space, activate a Bulgarian-made device to study the stars and other distant objects, try mixing metals and look for natural resources in Bulgaria.

Live black-and-white video broadcast on state-run Soviet and Bulgarian television Thursday showed the Mir complex - with its three solar battery panels shaped like an upside-down letter "T" - getting bigger and bigger as the Soyuz TM-5 capsule approached. Docking occurred shortly before 8 p.m.

About 90 minutes later, Soviet television broke into its evening news program "Vremya" for a live color broadcast showing Alexandrov, wearing a dark blue flight suit, aboard Mir with four Soviet cosmonauts.

Among those shown applauding the docking at the Soviet Mission Control Center in Kaliningrad, northeast of Moscow, was Georgy Ivanov, a Bulgarian who along with a Soviet cosmonaut failed in April 1979 to link a Soyuz-33 capsule with the Soviet space station Salyut-6.

Alexandrov was the backup Bulgarian cosmonaut for the 1979 mission and began training last year for the current mission, which is scheduled to end June 17. He and Soviet cosmonauts Viktor P. Savinykh and Anatoly Y. Solovyov blasted off Tuesday from the Baikonur Cosmodrome in Soviet Central Asia.

Aboard Mir, the three are guests of Soviet cosmonauts Vladimir Titov and Musa Manarov, who boarded the space station Dec. 23.

If the cosmonauts have any spare time, Mission Control's planning director Boris A. Sirotkin told reporters, they can listen to music tapes, watch movies on videotape or read books and newspapers.

The 1979 docking failed because a maneuvering engine aboard the Soyuz-33 malfunctioned. The docking was aborted.

The Soviet labor newspaper, Trud, said Wednesday that the cosmonauts aboard the capsule "could have become prisoners in orbit" because the same engine would have to be used to return to Earth. A backup engine also didn't work properly, but it was able to return the cosmonauts safely.

Soviet reports on the current mission have emphasized that the Soyuz capsule's propulsion systems have been improved since the 1979 failure.

The Mir station has been aloft since February 1986. It is the base to which several scientific modules, supply craft and cosmonaut transport craft have been attached. Soviet officials say it will be manned permanently.