The Justice Department filed suit yesterday against Rep. Charles Diggs (D-Mich.) in an attempt to force him to pay at least $240,000 in civil damages as a result of a payroll kickback scheme in which he was convicted last year.

The suit claims that Diggs unjustly enriched himself by inflating the salaries of his Capitol Hill employees by $120,228, and asks for double damages under the Federal False Claims Act. He also could be charged up to $2,000 for each of the false claims he is accused of filing.

Diggs was convicted on criminal charges last October and faces a six-to-30 month jail term. In that case and in the suit filed yesterday, Diggs was charged with giving pay raises to his employes and having them return the money to him so he could pay his personal bills.

Diggs was censured by the House late last month, but retained his seat in Congress after he agreed to pay back about $40,000 and apologized to the House. Later moves to expel him from Congress for his conduct were rejected.

The suit alleges that Diggs received more money illegally than the criminal case charged or the House accepted as settlement. Attorneys familiar with the Diggs case said that the higher figure wought in the suit reflects the lesser burden of proof necessary in civil-- as opposed to criminal-- cases.

It alleges that Diggs padded the salaries of six of his staff members over a three-year period, and either used the money to pay bills or used their services for his personal business, a failing Detroit funeral home that he since has sold.

Diggs, who is free on bond pending an appeal of his conviction, allegedly was in serious financial trouble when he began the kickback scheme. He also faces a $29,000 tax lien from the IRS for his alleged failure to pay income taxes on the payroll kickback money.