MOSCOW (AP) _ Two Soviets and the first Afghan in space blasted off from a Central Asian space center early Monday to join cosmonauts seeking an endurance record aboard the Soviet Union's orbiting space station Mir.

A Proton rocket carrying pilot Vladimir Lyakhov, doctor Valery Polyakov and Afghan military pilot Abdul Ahmad Mohmand aboard a Soyuz TM-6 capsule lifted off from the Baikonur space center at 8:23 a.m. Moscow time (12:23 a.m. EDT).

Soviet television provided a live broadcast of the white rocket riding a long orange flame into the clear sky, and cut away as the rocket disappeared. Lift-off was as scheduled.

While the Soviet cosmonaut and Afghan crew member will return to Earth after eight days, Polyakov will remain aboard Mir to monitor the health of its long-time residents, Vladimir Titov and Musa Manarov, officials said.

On Dec. 21, Titov, 40, and Manarov, 37, will have been in space one year, breaking the previous endurance record set by Yuri Romanenko. Romanenko returned to Earth from a 326-day flight on Dec. 29.

Soviet space officials have said Mir will be permanently manned, and replacements for Titov and Manarov are to be sent aloft in a joint Soviet- French space flight later this year, said Maj. Gen. Vladimir Dzhamidekov, deputy director of cosmonaut training at Baikonur.

His boss, Vladimir Shatalov, said Titov and Manarov will return to Earth in late December but did not give an exact date or say whether Polyakov will accompany them.

Soviet space officials have said the long flights are designed to test whether people can withstand weightlessness and the other conditions for a possible manned mission to Mars, a journey that would take three years.

With an Afghan spaceman on board, this week's flight has as much political as scientific significance.

The flight was originally scheduled for the middle of next year, but was moved up to Monday, apparently so it would fall near the halfway point in the Soviet withdrawal of troops from Afghanistan.

Radio Moscow reported Sunday that Mohmand, a 29-year-old veteran military pilot, was chosen from two candidates training to be the first Afghan in space.

Radio Moscow said the Soyuz TM-6 will dock with the Soviet Union's orbiting space station, Mir (Peace), on Wednesday.

Mohmand himself was part of the joint Soviet-Afghan effort to put down an insurgency in his homeland. He said in an interview published Sunday in the newspaper Sovietskaya Rossiya that he had flown 500 attack flights against insurgents.

The Soviet Union began pulling out its more than 100,000 troops from Afghanistan on May 15 and reached the halfway mark Aug. 15.

During the pullout, the Kremlin has flooded the official media with reports emphasizing that economic, scientific and cultural contacts will increase as Soviet-Afghan military links are scaled back.

Afghanistan highlighted the political significance of the joint mission by sending an official delegation headed by Mohammad Aslam Watanjar, Afghanistan's communications minister and member of its ruling Politburo, to Baikonur.

Science also figures prominently in the mission. Mohmand told Sovietskaya Rossiya the cosmonauts will use instruments aboard Mir to search for potential mining areas in his homeland and to measure oil and gas deposits.

To help alleviate a water shortage in Afghanistan, the cosmonauts also will be looking at snow and glaciers in mountains and will assess the hydroelectric potential of Afghanistan's rivers, Mohmand said.

The spacemen also will try to locate regions in Afghanistan where earthquakes might occur.

The 46-year-old Polyakov, making his first space flight, is to supervise experiments on the effects of space travel on the body.

The Afghan-Soviet mission is the second of three missions scheduled this year in the Soviet manned space program. It comes after the U.S. manned program was grounded after the January 1986 explosion of the shuttle Challenger. The shuttle Discovery is expected to be launched in late September or early October.

A Bulgarian cosmonaut and two Soviet colleagues returned to Earth June 17 after a 10-day flight that included a linking with Mir. A Soviet-French crew is to blast off Nov. 21 for a monthlong mission.