For more than three decades, astronomer and extraterrestrial life visionary Jill Tarter has been the public face of the sometimes controversial, sometimes lauded search for signs of intelligent beings throughout the cosmos.

A founding member in 1984 of the nonprofit Center for SETI (Search for Extraterrestrial Intelligence) Research, Tarter has led the group’s expansion and evolution as the broader science of astrobiology has blossomed.

To her great disappointment, she said last week, SETI has not detected the kind of compressed radio signals from afar that nature cannot create but intelligent beings can. Nonetheless, she said she is beyond delighted about how the search for life beyond Earth has become so much more sophisticated, more promising and more mainstream.

Yet Tarter and SETI announced Tuesday morning that its longtime director will step down from that post and turn her efforts to fundraising to keep the organization afloat. Tarter will hand over the director’s reins to Gerry Harp, an expert in quantum mechanics who has been an innovator in using the Northern California radio telescope array that SETI partially owns and has helped run.

Why the move now?

“When we started SETI, we had two goals in mind,” Tarter said, “to search for extraterrestrial intelligence, and to create a center where that search could continue into the future as our technologies, our understandings and our computing powers increased.

“The search is more robust now than ever, but the center is struggling financially. It needs somebody to spend all their time raising funds so the Center for SETI Research itself can be around to understand that signal we are confident will be sent.”

Tarter, 68, was the obvious choice to lead the fundraising effort. Well-respected and honored in the scientific community, she is also known in popular culture as Ellie Arroway, a young woman obsessed with extraterrestrial life, played by actress Jodie Foster in the 1997 movie “Contact.”

Tarter has also long been involved in outreach programs such as SETI@home, which encourages computer owners to help process SETI data on their machines, and has been the principal investigator for two elementary, middle and high school curriculum projects on “Life in the Universe” and evolution funded by NASA, the National Science Foundation and others.

The immediacy of the financial threat became clear last year. SETI and the University of California at Berkeley jointly operated a sophisticated radio telescope array built with $30 million donated by Microsoft founder Paul Allen and others, primarily from Silicon Valley. The array went into operation in 2007 — a dream come true for those involved in the SETI effort.

But the 42-dish array, which sits on federal lands in Northern California, had to be put into hibernation for six months because of a lack of money. SETI has been short of the $3 million a year it needs to operate the center and the array. The shortfall was in large part caused by cuts in the California state university system and diminishing donations. The Allen Telescope Array resumed operations last year after sufficient donations came in and additional money flowed in from the Air Force, which funded a study into whether the array could be used as part of its system to track satellites and space debris in low-Earth orbit.

In April, the nonprofit group SRI International, which has three decades of experience in operating radio telescope facilities for the federal government and the National Science Foundation, took over management of the Allen Array. SRI has a contract with the Air Force to track space debris, an increasingly important task as essential and costly satellites are at greater risk of collision with the growing amount of orbiting space junk.

Tarter said that SETI will be able to continue its operations at the array — at Hat Creek, between Mount Lassen and Mount Shasta — while the space debris tracking gears up.

Fascinated by the work of Frank Drake, a pioneer in the field, Tarter started her work on the search for extraterrestrial life in the mid-1970s. For some time she worked on a small NASA-sponsored program focused on that search.

The program was scheduled to expand in the early 1990s, but then-Sen. Richard H. Bryan (D-Nev.) effectively killed it, famously saying the federal government shouldn’t be spending money in the search for little green men and UFOs. (It wasn’t.) SETI wasn’t allowed to compete for federal funds from 1993 until the last years of the George W. Bush administration.

SETI’s work continued under the nonprofit SETI Institute in Mountain View, Calif. A primary focus now is to look for signals that might be coming from the stars with orbiting exoplanets that have been identified by NASA’s Kepler telescope.

The Kepler space observatory has already found more than 2,300 “candidate” planets, and its discoveries have led astronomers and planetary scientists to conclude that there are probably hundreds of billions of planets in the Milky Way alone. Tarter is a member of the science team working with the Kepler data streaming in.

“Kepler has dramatically changed and improved how we do our SETI searches,” Tarter said. “Before we were pointing at stars that just might have planets and moons, and now we know they’re out there. Very exciting.”

She said she’s also encouraged by the growing international interest in SETI observation. Under the initiative of Japanese astronomer and observatory director Shin-ya Narusawa, a worldwide SETI effort to commemorate the 50th anniversary of Drake’s first efforts brought in 27 institutions from 15 nations.

The idea for the Northern California radio telescope array was born of SETI’s desire to have dedicated telescope time all its own, coupled with the pioneering work of William “Jack” Welch, former director of University of California at Berkeley’s Radio Astronomy Laboratory and of the fledgling Hat Creek facility. That Tarter and Welch are married no doubt lent additional energy to the joint venture.

Tarter says she hopes her greater role in fundraising will allow the Allen Array to grow to its initially planned size, but more immediately to keep the Center for SETI Research up and running.

“If during my career we don’t detect a signal, I’ll be disappointed, but still optimistic it will happen some day,” she said. “But if the SETI project withers and we don’t have a center to take advantage of the new discoveries that are sure to come . . . then I’ll consider my work very much unfinished.”