Japan is asking Britain to buy its P-1 submarine-hunting jet in a deal that could top $1 billion, a major step in Prime Minister Shinzo Abe's push to arms exports after decades of self-imposed restrictions, people with knowledge of the proposal said.

Britain has not formally decided it will buy new maritime patrol planes, having canceled an order for nine built by BAE Systems in 2010 due to delays and cost overruns, and the P-1, made by Kawasaki Heavy Industries, would face stiff competition from Boeing's P-8 Poseidon, the three sources said.

Japanese officials raised the issue of London buying the P-1 to replace the British-made Hawker Siddeley Nimrod, which was retired in 2011, when they met their UK counterparts to discuss defense-equipment cooperation at the Farnborough Air Show near London in July, the sources said.