Men aged 25 and 34 were detained in Belfast after the off-duty constable discovered a bomb under his car at his home in the city on Sunday.
Senior officers have said the attack could have killed the policeman's wife and two young children.
Police Service of Northern Ireland assistant chief constable George Hamilton said. "If that officer had not checked under his car we would have been looking at a murder or multiple murders,"
In a separate incident, a pipe bomb was found close to the gates of a police station in Tandragee in Armagh, near the homes of elderly residents.
The booby-trap device in Belfast was recovered from under the officer's car partially intact and police hope forensic tests on the remains could identify those who made and planted it. Mr Hamilton said he was linking the attack to "anti-peace" dissident republicans, who have already murdered two police officers.
Police have been warning for months that republican militants remain determined to kill members of the security forces.
On November 1, prison officer David Black was shot dead as he drove along the M1 motorway on his way to work at the high- security Maghaberry jail.