WASHINGTON — The director of the F.B.I., James B. Comey, told lawmakers at a Senate hearing on Tuesday that Russian hackers had penetrated the Republican National Committee’s computer records, but he called it a “limited penetration of old R.N.C.” computer systems that were “no longer in use.”

Mr. Comey’s statement was significant because the committee said weeks ago that it did not lose data to the Russians because of its strong cybersecurity. President-elect Donald J. Trump has repeated that assertion and has also said weaknesses in Democratic National Committee systems had opened the way for their systems to be hacked.

While Mr. Comey did not go into detail, he appeared to be referring to a Russian-led attack on a contractor in Tennessee, Smartech Corporation, used by the Republican committee to host some of its websites and handle some lists of donors.