Thirty-five women and 16 children were among 324 illegal migrants rescued in one of the operations on Monday with help from a fishing boat, a navy statement said.
The migrants, from countries including Chad, Nigeria, Mali and Libya, were drifting in two inflatable boats about seven nautical miles from Zuwara near the Tunisian border after the engines failed, it said.
The coastguard also rescued 117 migrants, including five women and two babies, off the coast of Zawiya, west of the capital Tripoli, on Monday, doctor Abdel Aziz al-Misrati of the charity International Medical Corps told AFP.
Rocked by lawlessness since the NATO-backed 2011 uprising that toppled and killed longtime dictator Moamer Kadhafi, Libya has become a key transit country for illegal migration across the Mediterranean Sea.
The migrants often try to make the treacherous crossing on unseaworthy boats, hoping to reach Italy and make their way further inland in Europe and start a new life.