Two Soviet cosmonauts broke a 326-day record for endurance in space Saturday, and the official news agency Tass announced that a second try to launch the Soviet space shuttle will take place Tuesday.

The first attempt to launch the shuttle Buran, on Oct. 29, ended 51 seconds before scheduled lift-off when a piece of equipment on the launch pad failed to move away from the unmanned craft.Tass said the two cosmonauts on the space station Mir - flight commander Vladimir Titov, 41, and engineer Musa Manarov, 37 - broke last year's record established by colleague Yuri Romanenko.

Titov and Manarov were reported healthy with only small changes in their weight and muscle measurements.

Scientists worry about atrophy when humans spend long periods in zero gravity in space using just a fraction of their strength.

The Buran space shuttle is due to lift off at 6 a.m. Tuesday (8 p.m. MST Monday). If the unmanned double orbit is successful, officials will begin planning routine flights with a crew, Tass said.

However, Soviet authorities said the Buran and its sister ships will shoot off into space "no more than two to four times a year."

Tass did not clarify whether that meant each shuttle would fly only four times a year or whether the entire fleet would make just four flights a year.

Alexander I. Dunaev, director of the Soviet commercial space agency Glavkosmos, said several shuttles are under construction.

The Soviets have not said how many shuttles they plan to build. But they will continue to use simpler, less expensive rockets to put satellites into orbit and save the shuttles for repair and hauling cargo to the Mir space station.

Buran, which means "snowstorm" in Russian, will circle the Earth twice on its first flight and land at a specially constructed runway back at the Baikonur Cosmodrome in Soviet Kazakhstan in Central Asia.

"The cause of the delay has now been eliminated and the Energia (booster rocket) system with the Buran orbiter is undergoing pre-launch preparations," Tass reported.

The two cosmonauts on the space station Mir - Titov and Manarov - will get some company for their last month in orbit when two Soviet colleagues and a Frenchman join them Nov. 26, Tass said. On Dec. 21, Titov and Manarov will end their year in space by flying home with the French cosmonaut, leaving their two Soviet colleagues in space.

The U.S. record for the longest manned mission is 84 days, set in 1973 by astronauts Gerald Carr, Edward Gibson and William Pogue aboard space station Skylab.