A "fortress mentality" has developed in Victoria Police, with the force "moving back to the dark ages" in response to the threat of terrorism, former police chiefs have warned in an open letter to Victorians.

The group, led by retired chief commissioner Kelvin Glare, expressed concern the force was disengaging with the community in its fight against extremism.

"[Victoria Police] put out a a blue paper last year, saying that [they] ought to be more engaged with the community," Mr Glare said.

"Instead of becoming more engaged it seemed to myself and a group of like-minded former police that they were in fact withdrawing from community engagement."

The letter expressed concern that public edicts issued to combat the terrorism threat, such as police working in pairs, sent a message to would-be terrorists that they were having an impact.

"We note the recent instruction that police must work in pairs and wear protective vests on duty, not travel to and from home in uniform and not take police cars home or park them where police live," the letter read. "An edict promulgated in response to the perceived increased threat of terrorism. "We are of the view that this is a win for terrorists and sends the message that [Victoria Police] fears these barbarians. "This is completely the antithesis of what community leaders from the Prime Minister and Premier down, are urging the community to do, be alert not alarmed. "Present and past serving police can rightfully feel offended as they have all served and will continue to serve their sworn duty to protect the citizens of this state. "This capitulation is at a time when [Victoria Police] ought to be providing leadership and setting an example that terrorism can never win in Australia."

Mr Glare said he believed any tightening of police security should have been done discretely within the police system.

"Those things, apart from anything else, ought not to be announced publically, they ought to be done privately within the confines of the operation of the police force," he said.

"To put a public message out there that we're concerned about you few people who are violent jihadists, isn't the right sort of message to be sending."

Victoria's acting chief commissioner Tim Cartwright has dismissed the criticism saying "the force is absolutely committed to community engagement".

"To suggest we've moved away from community engagement and youth engagement is absolutely wrong. It couldn't be more wrong," he said.

"For us the challenge is keeping our people safe but having our people welcoming to all sectors of the community.

"It's not giving into terrorism it's keeping my people safe while we keep the community safe."

'Basic policing' fundamentals going unheeded

The letter also criticised police leadership for moving towards larger police stations.

"This siege mentality will force police members to a further disconnection from the community," the letter read. "A basic policing tool is the gathering of information which can only occur through engagement with the community. "Without it policing becomes ineffective and crime and social disorder flourishes. "The fundamentals of good policing are being increasingly unheeded."

Mr Glare said withdrawal of policing programs aimed at youth engagement, such as the Police in Schools program, was a prime example of where the force had gone wrong.

"It was getting to young people before they get into trouble, teaching them not only do they have rights, but they have corresponding obligations and responsibilities, and teaching them to consider the consequences of their actions before they did something rather than having to deal with problems afterwards," he said.

"That was a very strong program doing a lot of good, and in the view of myself and my colleagues, it needs to be reintroduced."

The letter called for "an urgent independent review" of policing policy in the state.