A Soviet Soyuz spacecraft blasted off through clear skies over the central Asian republic of Kazakhstan today, carrying two cosmonauts to a mission on the orbiting space station Mir.

The launch was covered live on television, which, combined with last week's successful Vega probes of Halley's Comet, demonstrates new Soviet confidence in the nation's space program, according to western observers here.

The memory of the January explosion of the U.S. shuttle Challenger, in which seven American astronauts were killed, kept Soviet viewers close to television screens during today's broadcast.

It was the first live telecast of a Soviet launch with the exception of three missions involving astronauts from other nations. The Soviet Union, which readily broadcast a videotape of the Challenger explosion, has been reluctant to show the risky parts of Soviet missions on live television or to publicize Soviet space tragedies.

Leonid Kizim and Vladimir Solovyov took off from the Baikonur space center and are scheduled to dock their Soyuz T15 spacecraft with Mir (Peace) on Saturday, according to the official news agency Tass. Mir was launched three weeks ago. The Soyuz T15 is the first manned Soviet space mission in 1986.

The launch was broadcast on Soviet television at 3:33 p.m. local time (7:33 a.m. EST).

The 25-minute broadcast showed the two cosmonauts preparing hours before the flight, waving as they entered the spacecraft and communicating with ground crew after takeoff.

It showed the Soyuz T15, trailed by a tail of yellow and orange, blasting across the sky, and then quickly showed the two cosmonauts strapped inside.

A voice saying, "Flight on course, flight on course," was aired at regular intervals.

Portions of the launch were rebroadcast on the evening news program.

Kizim, 45, is the crew commander. An Air Force colonel, he is now on his third space flight. Solovyov, 40, deputy mission director at the mission control school near Moscow, is on his second.

Both men went on the record-breaking 237-day space expedition aboard the Salyut 7 space station in 1984.

After docking their spacecraft with Mir, the two will conduct scientific and technical studies and experiments, Tass said.

[James Oberg, an American space engineer and author of books on the Soviet space program, said in Houston that the launch broadcast was part of a new "openness policy" by the Soviet Union, The Associated Press reported. Oberg said he also expects the Mir to be linked this weekend with two other modules already in orbit, the Salyut 7 space station launched in 1982, and the Cosmos 1686, launched last fall. These two units already have been joined and are in an orbit just four miles above the Mir orbit, he said.]

The three previous Soviet launches that were broadcast live were the joint mission with Apollo in 1975, a mission with a French cosmonaut aboard in 1982 and one with an Indian aboard in 1984.