Hi, @DJCLARK10.
The Social Security Administration has a document titled How Work Affects Your Benefits. On the middle of page 4 it says: "We do count an employee’s contribution to a pension or retirement plan, however, if the contribution amount is included in the employee’s gross wages." I can't find anything specific, but I surmise they use Box 3 of your W2, which would include your retirement contributions.
In summary, no, contributing to your 401(k) will not decrease your earnings for purposes of the Social Security reduction for taking early benefits and continuing to work.
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