The explosive device was found outside the policeman's home in the Upper Newtownards Road area at around 2pm on Sunday.
Officers said they believed the bomb had been left there within a 48 hour-period of its discovery and said it was "clearly intended to kill".
PSNI Assistant Chief Constable George Hamilton said the bomb was detected before it exploded as the officer checked under the vehicle.
"We know that the officer parked his car at his home on Friday afternoon on the Upper Newtownards Road, the car hadn't been in use across the weekend," ACC Hamilton explained.
"He and his family were intending to use it yesterday, at around 2pm to go out for Sunday lunch. The officer checked his car and found the device under it, thankfully, before his wife and children got into the vehicle.
We’re grateful and I’m sure the officer is as well, that he went to the extent of checking his car because had he not, we believe the consequences would have been absolutely devastating for the officer, his family, for the police family and actually for the communities across Northern Ireland.
ACC George Hamilton
The man is understood to be a serving PSNI officer of 16 years who had previously served with the RUC Reserve.
Several homes were evacuated in the Upper Newtownards Road area as army bomb squad officers made the area safe on Sunday.
First Minister Peter Robinson said the murder bid was "an outrage".
"I think everyone right across Northern Ireland would be appalled at the behaviour of the dissident terrorists," he said.
"I think there is a particular issue in and around east Belfast, it's the second similar type of offence that has occurred and it clearly indicates that there is someone or some group in and around the area trying to spot police officers."
Mr Robinson urged that those working in the PSNI should be particularly careful and to be on "special alert".
Terry Spence, Chairman of the Police Federation for Northern Ireland said the officer's vigilance saved his life and the lives of his family.
"I think it's very clear that today, on the eve of 2013, we could have been mourning the death of a constable in the PSNI, his wife and his two young children.
"Since the beginning of this year there have been 86 gun and bomb attacks which can be attributed to dissident republicans in Northern Ireland. That's why we're calling again for an additional 1000 police officers, it's the bare minimum that we need to see off this threat."
Justice Minister David Ford said the attempted murder was an "attack on our whole community".
As we approach a new year filled with promise in terms of the events we are hosting, I call on all those with any role in, knowledge of, or influence over those promoting acts of terror to recognise they do not have the right to intimidate, murder or in any other way to seek to undermine the democratic process.
Justice Minister David Ford
"The people responsible for this and other recent attacks have no mandate and speak for no-one. They need to recognise the futility of their campaign and respect the wishes of the vast majority of our community who want an end to all violent acts."
Sinn Féin South Belfast MLA Alex Maskey said the planting of the device under the policeman's car was "an attempt to kill for killing sake".
"These actions will achieve nothing except bring misery and hurt to another family. Thankfully no one was hurt in this incident," he said.
"The people responsible or their spokespeople need to come forward and explain how these type of actions are going to advance the cause of Irish unity. They need to catch up with the rest of the people of Ireland and cease these futile actions.
"The Irish people voted for the peace process and Sinn Féin will remain focused on delivering the necessary change through democratic and peaceful means."
Bombing attempts like this are the actions of militarists who are attempting to kill for the sake of killing. They have no strategy and no support from the people of Ireland who have voted for change to be made through the democratic process.
Alex Maskey, Sinn Féin MLA
Ulster Unionist Policing Board Member, Ross Hussey MLA said he was thankful that the officer and his family escaped injury.
"As events unfolded on Sunday, we saw the evil intention of the cowards who planted a bomb under the PSNI Officer's car in east Belfast," he said.
"These republican terrorists not only showed a callous disregard for the sanctity of life in attempting to murder a public servant, but they also showed the depths to which they are prepared to plunge. We could have seen a whole family wiped out."
SDLP Policing Board member Conall McDevitt condemned the murder bid as a "cynical and deplorable" attempt to target an officer.
Police have made a specific appeal for information from anyone who was in the area from Friday evening.
Senior Investigating Officer Detective Inspector Dickson said members of the public may have seen something which could help the investigation.
"At this stage we believe that the device was left underneath the officer's car sometime between 5:30pm on Friday 28 December and 2pm on Sunday 30 December," he said.
"My investigation team want to speak to anyone who was in the area of the Upper Newtownards Road between the junction of the Knock Road and Knockdene Park.
"While traffic may have been quiet because of the holiday season, it is entirely possible that a taxi driver or dog walker may have seen something untoward in that area, like a parked vehicle or someone acting suspiciously."