The items, which were bought at a Christie's auction last summer, are priced at £122,500 for the dagger, or 'jambiya', and £12,500 for his traditional Arab robes.
Culture minister Ed Vaizey levied the export bars to keep these "classic objects" in the UK, following a recommendation by the Reviewing Committee on the Export of Works of Art and Objects of Cultural Interest, which declared the objects to have close association with British history and national life.
The dagger was given to the British diplomat by Sherif Nasir in 1917, and the traditional Arab robes are the costume Lawrence wears in his 1919 portrait by Augustus John.
Ferdinand Bol Portrait
Another item currently under export ban is Ferdinand Bol's Portrait of a Boy, thought to depict the artist's son, which was bought by an Asian collector at Sotheby's in July.
Unless the asking price of £5.2m can be matched it will be lost to the nation.
On display in Castle Howard, North Yorkshire, since 1825, the painting was deemed of "aesthetic importance and outstanding significance" by the reviewing committee and they recommended deferring the export licence.
Vaizey added that the painting has been present in the country for more than 200 years and is the finest example of Dutch Golden Age work left in the UK.