The wheat should contain 12.5 percent protein and will be for shipment from Sept. 1-30, SAGO said in a statement.
The deadline for offers is Friday, it said.
Of the total, 180,000 tonnes will be for shipment to the port of Jeddah and 120,000 tonnes to the port of Dammam.
Saudi Arabia has become a major importer of hard and soft wheat since abandoning plans for self-sufficiency in 2008 because farming in the desert drained scarce water supplies. It halted purchases of locally grown wheat this year.
The tender is the third to be announced in 2016.