Let $ABCD$ be an isosceles trapezoid with bases $AB = 92$ and $CD = 19$.  Suppose $AD = BC = x$ and a circle with center on $\overline{AB}$ is tangent to segments $\overline{AD}$ and $\overline{BC}$.  If $m$ is the smallest possible value of $x$, then $m^2 = $

$ \textbf{(A)}\ 1369\qquad\textbf{(B)}\ 1679\qquad\textbf{(C)}\ 1748\qquad\textbf{(D)}\ 2109\qquad\textbf{(E)}\ 8825 $
1. **Diagram and Setup**: Consider the isosceles trapezoid \(ABCD\) with \(AB = 92\) and \(CD = 19\). Let \(AD = BC = x\). A circle with its center on \(\overline{AB}\) is tangent to \(\overline{AD}\) and \(\overline{BC}\). To minimize \(x\), we need to consider the configuration where the circle is tangent to \(AD\) and \(BC\) at points \(D\) and \(C\) respectively.

2. **Midpoint and Altitude**: Let \(M\) be the midpoint of \(AB\), which is also the center of the circle. Drop a perpendicular from \(D\) to \(AB\) and let the foot of this perpendicular be \(E\). Since \(M\) is the center of the circle, \(ME\) is the radius of the circle and is perpendicular to \(AD\) at \(D\). Thus, \(\angle ADM = 90^\circ\).

3. **Calculating Segments**: 
   - The length \(AE\) is half the difference between \(AB\) and \(CD\):
     \[
     AE = \frac{AB - CD}{2} = \frac{92 - 19}{2} = \frac{73}{2}
     \]
   - The length \(EM\) is half the length of \(CD\):
     \[
     EM = \frac{CD}{2} = \frac{19}{2}
     \]

4. **Using the Pythagorean Theorem**: In the right triangle \(\triangle ADE\), we have:
   \[
   AD^2 = AE^2 + DE^2
   \]
   Substituting the known values:
   \[
   x^2 = \left(\frac{73}{2}\right)^2 + \left(\frac{19}{2}\right)^2
   \]

5. **Simplifying the Expression**:
   \[
   x^2 = \frac{73^2}{4} + \frac{19^2}{4}
   \]
   \[
   x^2 = \frac{73^2 + 19^2}{4}
   \]
   \[
   x^2 = \frac{5329 + 361}{4}
   \]
   \[
   x^2 = \frac{5690}{4}
   \]
   \[
   x^2 = 1422.5
   \]

6. **Revisiting the Calculation**: The previous steps seem to have an error. Let's re-evaluate the correct approach:
   - The correct approach should involve the product of the segments:
     \[
     DE^2 = \frac{73 \cdot 19}{4}
     \]
   - Then:
     \[
     x^2 = \frac{73^2}{4} + \frac{73 \cdot 19}{4}
     \]
     \[
     x^2 = \frac{73(73 + 19)}{4}
     \]
     \[
     x^2 = \frac{73 \cdot 92}{4}
     \]
     \[
     x^2 = 73 \cdot 23
     \]
     \[
     x^2 = 1679
     \]

The final answer is \(\boxed{1679}\)