MOSCOW-The Soviet Union launched a third manned spacecraft early Monday leaving seven Russian cosmonauts circling the Earth.

Soyuz 8, manned by two experienced space pilots, lifted off from the Baikaonur cosmodrome in Soviet Central Asia to join Soyuz 6 and Soyuz 7, which were sent aloft on Saturday and Sunday.

Soyuz 6 has special welding equipment on board apparently to be used to construct a manned orbiting platform after the thrice vessels link up in space. Some of the cosmonauts could stay behind to man the station while the others returned to earth and new crews could be sent up as relief, American experts theorized.

This country does not plan to construct its own space station until 1972, concentrating in the near future on further flights to the moon.

Safe With Daddy

EAST MEADOW, N.Y.-Julie and David Eisenhower will spend Wednesday, the day of the nation-wide Moratorium, in the White House to avoid any trouble.

A White House spokesman in Washington said it had been decided that the two 21-year-old college seniors should spend the day in the nation's capital to avoid any trouble.

President Nixon's son-in-law yesterday said that Julie's Wednesday classes at Smith, and his at Amherst, were "called off at the discretion of the teachers."