The US government agencies that defend the nation are in the midst of a charm offensive -- trying to win over the hearts and minds of Silicon Valley's tech workers.

The move is evoking considerable skepticism from the US tech community.

In recent months, the US Defense Department and Department of Homeland Security have announced the opening of Silicon Valley offices as part of an effort to mend fences.

Relations have worsened since the 2013 leak of classified documents by former National Security Agency contractor Edward Snowden and disputes over issues ranging from encryption to surveillance.

"I believe we must renew the bonds of trust and rebuild the bridge between the Pentagon and Silicon Valley," Defense Secretary Ashton Carter said in an April speech in California.

Carter unveiled a "Defense Innovative Unit Experimental" to work with the private sector, enabling startups to work with the Pentagon, and a program that allows technology workers to toggle back and forth between the civilian and military.

Homeland Security chief Jeh Johnson meanwhile also went to California to announce a Silicon Valley office "to serve as another point of contact with our friends here" and "to convince some of the talented workforce here in Silicon Valley to come to Washington."

The new "US Digital Service," Johnson said, "provides the option for talent to flow and rotate between private industry and our government teams."

NSA director Michael Rogers has been making the same pitch, saying he wants students and new university graduates to understand the agency's "ethos and culture" and the possibilities for "an amazing mission."

"The biggest challenge is not retaining people," Rogers said in a Washington speech. "The biggest challenge is getting people in the door in this environment."

- 'A brick wall' -

The efforts have been greeted with at best a lukewarm response from the tech community.

"They are going to hit a brick wall because there is a fundamental misalignment between the expectations of the federal government and those of Silicon Valley," said Anup Ghosh, founder of the cybersecurity firm Invincea and a former program manager at the Pentagon's Defense Advanced Research Projects Agency (DARPA).

In the race for talented tech personnel, Ghosh said, the federal government is ill-equipped to compete with the likes of Facebook, Google and others, which pay far more generous salaries and offer a different lifestyle.

"The government does not have many tools to recruit these Silicon Valley A-listers," he said.

"I don't think they could recruit West Coasters to come in with the federal service, even if there is a West Coast office."

Rob Enderle, a Silicon Valley consultant and analyst at Enderle group, said the trust gap is higher than ever.

"Nobody here trusts the government when it comes to this stuff, and sending government officials here after the Snowden leaks is probably more of a theatrical event than about moving hearts and minds," Enderle told AFP.

John Dickson, a former air force intelligence officer who is now a partner with the security consulting Denim Group, said the two cultures are far apart and that the Snowden revelations have made matters worse.

The revelations about US snooping have "done substantial damage to (the government's) ability to recruit people," Dickson said.

"It has created distrust, especially among millennials, and I think it will take a while to change."

- Restoring trust -

Roger Kay, analyst and consultant and Endpoint Technologies Associates, said US intelligence agencies have historically had people with strong technical skills but that as technology evolves, "it's obvious the NSA needs the best people."

"Because of the sheer complexity of the crypto world, they need the best engineers," Kay said.

"Some of their stuff has gone dark because of Snowden and they need to light that up again."

But Kay said that many in the tech community are mistrustful of the NSA and that "most of the people I know would pick Silicon Valley" over a government job.

Kay said the best approach for US agencies is to appeal to the patriotism of potential job candidates, but that they need to implement real reforms to improve their image.

Daniel Castro, vice president at the Information Technology & Innovation Foundation, a Washington think tank, said reforms should include more transparency and oversight of intelligence agencies.

"It's not that they are not going to do surveillance," he said.

"But they have to be very focused and targeted on the bad guys. That's a compelling mission. If they can retool and refocus in that way, it could help."