The nation’s tax collectors announced Thursday that three companies would help collect unpaid tax debts.

The firms, chosen from 33 applicants, will help the Internal Revenue Service collect money from taxpayers who agree they owe taxes but haven’t paid. As much as $7.7 billion in unpaid taxes could be eligible for assignment to a private debt collector, debts the IRS does not have the resources to collect itself.

Congress in 2004 gave the IRS authority to contract debt collection to private companies. The tax agency plans to expand the limited trial, which will be under way this summer, to as many as 10 companies in 2008.

The three chosen firms are The CBE Group Inc., in Waterloo, Iowa; Linebarger Goggan Blair & Sampson LLP in Austin, Texas; and Pioneer Credit Recovery Inc. in Arcade, N.Y.