MOSCOW (AP) _ Three Russian cosmonauts blasted off Saturday for a rendezvous with the Mir orbiting space station, and one of them may set a new record for living in space.

The Soyez TU-18 rocket lifted off flawlessly and went into orbit with no problems, Mission Control spokesman Alexander Volchenkov said nine hours into the flight.

The troubled Russian space program has a lot riding on the mission, the 15th since the Mir was launched in 1986. The launch had been delayed for two months because of a shortage of booster rockets.

''This is definitely one of the most critical flights in a long time because of doubts about their capabilities,'' Houston-based space expert James Oberg said in a telephone interview.

The rocket rose from a snowy launch pad at the Baikonur cosmodrome in the former Soviet Central Asian republic of Kazakhstan. Russian television showed it quickly disappearing into a thick cloud cover.

The United States and Russia signed an agreement in December bringing Russia into an international space station program. A representative of NASA was present at the launch, the television report said.

The spaceship was to dock Monday with the Mir for a crew change. The current Mir crew will come home Jan. 15 after 200 days in space.

Two members of the new crew will stay on the station until July 4.

The third, 51-year-old physician Valery Polyakov, will try to stay for 427 days to break the record of 366 days set by cosmonauts Vladimir Titov and Musa Manarov in a mission that ended in December 1988.

''See you - in a better world,'' Polyakov joked from the launch pad, then added: ''Here's to overcoming our problems on Earth and to keeping our space program on top 3/8''

The Russian space program has fallen on hard times since the 1991 collapse of the Soviet Union. It has been plagued by funding problems and disputes over control of Baikonur.

Oberg noted the short overlap of the two crews on Mir and said it suggested concern about the capsule that will bring back the old crew. He described the spacecraft as ''older than preferred'' but said the ''risks are minimal.''

The new mission will focus on medical research, the ITAR-Tass news agency said, and no space walks are planned.

The U.S.-Russian deal, worth $400 million to Russia over the next four years, calls for up to 10 U.S. shuttle flights to the Mir.

Eventually, Russia will join the United States, Japan, Canada and the European Space Agency in building an international space station.