12. (6 points) Fill in each of the seven small circles in the figure with a natural number, while satisfying the following requirements:
(1) Make the sum of the seven natural numbers filled in 1997;
(2) Make each number given in the figure the difference between the numbers filled in the adjacent two $O$s.
【Solution】Solution: Let the top number be $A$. According to the problem:
Since the sum of numbers from 1 to 7 is 28, the sum of the numbers with plus signs is 14, and the sum of the numbers with minus signs is 14;
Thus: $1 - 2 - 3 - 4 - 5 + 6 + 7 = 0$, which means:
$$
A + 1 - 2 + 3 + 4 - 5 + 6 - 7 = A \text{, }
$$

Therefore, the seven numbers are $A, A+1, A+1-2=A-1, A+1-2+3=A+2, A+6, A+1, A+7$, so: $7A + 16 = 1997$,
$$
A = 283 \text{. }
$$

Thus, the numbers are $283, 284, 282, 285, 289, 284, 290$.
Answer: The top number is 283, and in a clockwise direction, they are: $283, 284, 282, 285, 289, 284, 290$.