If you’re a Jackie O. fan with a few million bucks to spare, this auction is for you.

The letters, sketches and even fabric swatches sent back and forth between the stylish former first lady and her favorite designer, Oleg Cassini, are expected to head to the block — part of the government’s bid to recoup at least part of a $51 million penalty racked up by Cassini’s currently jailed widow, Marianne Nestor.

The 68-year-old Nestor is accused of robbing her dead husband’s companies and refusing to begin making restitution.

One letter on Cassini stationary includes Jackie O’s dress measurements — a 35 1/2-inch bust, 26-inch waist and 38-inch hips — with a Western Union telegram that reads, “Have told Bergdorfs to send you my measurements. Long letter follows. Jackie.”

The East 19th Street manse also holds a $60,000 suit of armor that once belonged to William Randolph Hearst and a $175,000, 15th century altarpiece depicting five saints on carved, gilded wood.

A lawyer for Nestor did not return calls for comment.