Peers said little had been heard about security outside the Olympic Park
The EU should be involved in security planning for the 2012 Olympics and be ready to assist if there is a terrorist attack, says a committee of peers.
Ministers should contact the monitoring and information centre (MIC), which co-ordinates EU response to emergencies, "without delay", the EU committee said.
And security should be focused on the five host boroughs, not just the Olympic Park area, the peers said.
The government said it was committed to ensuring a safe and peaceful games.
Ministers have previously pledged to stick to a £600m security budget for the Games.
The Lords European Union committee is due to publish its report urging greater co-operation between the EU and Nato on disaster responses.
The MIC has long experience of putting European teams on standby for sporting events.
Portugal asked for chemical, biological, radiological and nuclear decontamination teams to be kept on standby during the Euro 2004 football championships.
Committee chairman Lord Jopling said: "It is increasingly clear that the 2012 Olympics could be a prime target for terrorists.
"It is vital that the government takes every possible step to ensure that other EU member states are fully prepared to assist the UK in the case of a potential attack.
"We are surprised that this process is not already in hand and we recommend the government begin liaising with the MIC as a matter of urgency."
The committee said much of the interest had been focused on security for the Olympic Park in east London but little had been heard about the five boroughs involved in hosting events which were "at least as vulnerable".
The report said: "We do not believe that it is too soon to involve the MIC in preparations for security issues, not just within the Olympic venue but also in the surrounding boroughs.
"We urge the government to contact the MIC without delay to begin work on back-up support for our own national security arrangements, even if a formal request for assistance is not needed until nearer the time."
A Home Office spokesman said the government was committed to taking "all the financial, planning and operational measures necessary to ensure a safe and peaceful 2012 Olympic and Paralympic Games".
He said the Games' "safety and security strategy" had been approved by ministers last month and developed by government agencies, security and emergency services and Olympic-organising bodies.
And he said the security strategy would continue evolving as work continues on the Olympics infrastructure.