Federal prosecutors recommended on Thursday that two top leaders of the far-right Proud Boys convicted of seditious conspiracy in the Jan. 6 attack on the Capitol be sentenced to 33 years in prison, the stiffest penalties requested so far out of more than 1,000 people charged in the sprawling investigation.

In seeking to severely punish the two Proud Boys, Enrique Tarrio, the former chairman of the group, and Joseph Biggs, one of Mr. Tarrio’s top lieutenants, prosecutors asked the judge in the case to increase their sentences with what is known as a terrorism enhancement.

“The defendants understood the stakes, and they embraced their role in bringing about a ‘revolution,’” the prosecutors wrote in a 155-page filing to Judge Timothy J. Kelly of the U.S. District Court in Washington. “They unleashed a force on the Capitol that was calculated to exert their political will on elected officials by force and to undo the results of a democratic election.”

“The foot soldiers of the right aimed to keep their leader in power,” the prosecutors continued, referring to former President Donald J. Trump. “They failed. They are not heroes; they are criminals.”