You may be eligible to a tax treaty on your US source income, however you cannot claim reduced tax rate if you do not have US TIN (SSN/ITIN). Therefore you will be taxed at non-reduced tax rate. Normally, this is the tax rate you would be taxed if no tax treaty applies to your income.
Info: Once you obtain a taxpayer ID (SSN or ITIN) you can still claim the tax treaty on your tax return.