WASHINGTON — His entire involvement in the presidential campaign has consisted of four words uttered to a reporter as elevator doors were closing: “I’m for Mitt Romney.” But former President George W. Bush gingerly enters the fray a little more this week with a new book outlining ways to rebuild the economy.

For the first time since leaving office three and a half years ago, Mr. Bush is advancing a variety of ideas about how to jump-start economic growth by restructuring taxes, expanding trade, encouraging innovation, fixing immigration and overhauling Social Security. He wrote the foreword for the book, a collection of essays from an array of economists, including five Nobel Prize winners, and he proposes a national goal of expanding the economy by 4 percent a year on a sustained basis.

“The 4% Solution: Unleashing the Economic Growth America Needs,” to be unveiled by the former president in Dallas on Tuesday and published by Crown Business, is neither campaign template nor partisan screed. It is a wonky paean to free enterprise.

It is also the next step in a gradual return to the public stage by a president who has largely remained out of the limelight since turning over the White House to President Obama. Mr. Bush has repeatedly said his successor deserves his silence and has largely avoided commenting on current affairs. He has not publicly appeared with Mr. Romney to endorse him, as his parents have done, or hosted a fund-raiser for Mr. Romney, as his vice president did last week.