The two leaders will announce plans for French planes to use British refuelling aircraft The UK and France are to sign a treaty agreeing to the joint development and testing of nuclear warheads.
The plans will see one centre set up in the UK to develop technology and another in France to carry out testing.
Prime Minister David Cameron and President Nicolas Sarkozy will also outline plans, at a London summit, for a joint army expeditionary force.
Downing Street called the measures “practical”, but Labour said they left “big questions” over the UK’s defences.
A Downing Street spokesman said: “This summit marks a deepening of the UK-France bilateral relationship. Ours is now a strategic partnership tackling together the biggest challenges facing our two countries.”
The summit comes two weeks after the UK government announced cuts to its armed forces, in the first strategic defence review since 1998, as part of savings aimed at reducing the country’s budget deficit.
Mr Cameron and Mr Sarkozy are to sign two treaties – one on greater general military co-operation and the other on nuclear weapons.
The latter will set up a centre in the UK to develop technology and another one in France to carry out the testing.
It is understood that each country will still control its own warheads, and that nuclear secrets will not be shared.
The other treaty will allow the setting up of a “combined joint expeditionary force”, thought to involve a brigade of about 5,000 soldiers from each side.
Each country will retain a veto for each operation, which will operate under one military commander to be chosen at the time.
The UK and France have also agreed to keep at least one aircraft carrier at sea between them at any one time.
Each will be able to use the other’s carrier in some form, certainly for training and possibly operations.
Meanwhile, France is to use British A400M fuelling aircraft when there is spare capacity, with plans in place for common maintenance and training.
Joint work on drones, mine counter-measures and satellite communications is also proposed.
Mr Cameron told MPs on Monday: “I do seriously believe that this link-up with the French over defence is in the long term interests of both our countries.
“And to those who worry that this might in some way lead to… European armies, that is not the point. The point is to enhance sovereign capability by two like-minded countries being able to work together.”
Shadow defence secretary Jim Murphy said: “I support the government’s emphasis on international co-operation, taking forward the good work of the last government.
“We share common threats with countries such as France, from terrorism to privacy to cyber-attack. Deepening military ties is an essential part of modern defence policy.
“Interdependence, however, is different from dependence, and binding legal treaties pose some big questions for the government.”
Mr Murphy also questioned whether the the UK was entering “an era where we are reliant on our allies to fill in the gaps in the government’s defence policy”.
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