A large philanthropy is renewing efforts to back a think tank that has helped shape federal retirement legislation.

The Pew Charitable Trusts, Philadelphia, says it will contribute $3.5 million more to the Retirement Security Project, New York, a 2-year-old policy research organization that has been trying to use research to develop practical proposals for increasing U.S. workers’ savings rate.

The RSP has played an important role in encouraging employers to enroll employees in 401(k) plans automatically and to persuade Congress to extend the Saver’s Credit past 2006, Pew says.