Federal scientists are on the General Schedule payscale. As mentioned in another comment, they start out at about a GS-12 for PhD-level positions and move up to GS-15 from there (and then a small number of highly influential scientists can become 'super scientists' at the GS-16 level, and a very select few, i.e. Fauci, are on RF rather than GS scales). Then there is a locality adjustment.

This is the table with the DC locality adjustment: https://www.fedweek.com/pay-tables/2021-gs-pay-table-washing...

The rates are pretty similar to professor salaries at research universities; staff scientists at universities are often subordinate or soft-money positions.