Gary Humphries in his Parliamentary office ahead of his valedictory speech tomorrow.

Gary Humphries in his Parliamentary office ahead of his valedictory speech tomorrow. Photo: Melissa Adams

Opposition Leader Tony Abbott will be given a stern lecture on Wednesday - by one of his team - to respect the public service rather then treat it like ''the enemy''.

Outgoing ACT Liberal Gary Humphries will bluntly say a Coalition government will regret any decision to cut sharply into the public service.

''As they look to make government leaner and meaner, they have to be very careful that they don't wither the capacity to deal with the big challenges of a Liberal government's agenda by getting so many people out the door that they suddenly find themselves incapable of delivering what they promised,'' Senator Humphries said on Tuesday evening.

"They have to be aware the public service is an asset to be looked after like a car - you've got to make sure it's oiled and properly fuelled and looked after.

"Without that sense of the value of the public service to a Liberal government, they will be in trouble.''

Senator Humphries will deliver the lesson for an incoming Coalition government to respect the public service as ''a crucially important national asset'' when he gives his valedictory speech on Wednesday.

"They need to make sure it's professional, properly resourced and motivated and is trusted because, as a government, they will absolutely depend on having a public service which is full of those things to deliver whatever we promise to do at the election,'' he said.

"Sometimes it's easy to think of the public service as being part of the government of the day, part of the enemy - we can't afford to fall into that track.

"I'm going to remind my colleagues that they need to think of the public service in a positive and constructive way.''

When Senator Humphries says goodbye to the Senate, he intends to turn the abrupt end of his political career into a positive.

He knows he is young enough - 55 next month - to pursue a third career but does not intend to accept a diplomatic post if the Coalition wins the election.

Instead, he has his eye firmly on embracing a role in Canberra developing public policy.

This year Senator Humphries lost a preselection contest to Zed Seselja, who had given up the role as ACT opposition leader to move into federal politics.

Federal Opposition Leader Tony Abbott stood firmly by Senator Humphries during the contest and will speak at a farewell function for the ACT senator on Wednesday evening.

Senator Humphries said he would never be happy about the circumstances of the preselection battle but he was focused on defeating Labor.

''I want an end to the charade of Labor government more than I wish any ill will towards Zed,'' he said.

''I want him to succeed and be the next Liberal senator because I want the Coalition to have the numbers to do what it needs to do in the next Parliament.

''I'm not going to step away from the opinions I expressed about the process of the preselection, but it's yesterday's story.''

Senator Humphries should be entitled to a lifelong pension of about $80,000 a year when he leaves the Senate in September.

His speech will cover his decade in the Senate as well as his time in the Legislative Assembly, where he was not able to deliver a valedictory speech. He says the stand-out highlight of his Senate career was being part of inquiries into mental health and the forgotten Australians. ''These key inquiries led to lots of extra dollars for mental health and to the apology to the forgotten Australians,'' he said.

''Those are things that really made a big difference in people's lives and I feel a lot of sense of satisfaction about that.''

From his time as Chief Minister, Senator Humphries nominates the highlight as the creation of an ACT helicopter rescue service, against public service objections to the cost.

''When we came to office in '95, the department said you can't achieve a rescue helicopter service, it ain't going to happen, and I said, yes it is going to happen, and three years later, it did,'' he said. Senator Humphries, a solicitor before politics, will return to the private sector. ''I think it's important to be able to make my own way and I've been on a government payroll of one sort or another for a quarter of a century,'' he said. ''I've had some offers from people to work in areas to do with public policy and that's exciting. It'll be based in Canberra, it'll be public policy based, but which of the options in that mould I choose is a decision I'm yet to make.''