That can be complicated. I want to refer this to another expert, @pk
If there is a tax treaty with the other country, there are two ways to treat a government pension/social security plan.
1. Follow the laws of the other country in paying income tax on the social security benefit in that country. If you do that, then it is not taxable at all in the US and does not have to be reported on your US tax return. (This is relying on the treaty.)
2. If you choose not to follow the laws of the home country, then you report it as "miscellaneous/other taxable income" on your US tax return.
Obviously, what works best for you depends on the laws of your home country regarding paying tax on the social benefit.