The industry supplies 10% of manufacturing jobs in the UK
Investment in defence research and technology must be maintained to protect the industry, its trade body has warned in two reports.
The Defence Industries Council has published two reports amid fears spending could face major cuts in the next Ministry of Defence review.
The DIC says investing in the industry will help protect the country and could provide a "path out of recession".
The sector currently employs 300,000 people in the UK.
It also generated an annual turnover of £35bn in 2008.
The Ministry of Defence review will decide the future direction of defence after the next general election.
One of the DIC's reports examines the economic contribution the defence industry makes to the UK, while the second focuses on the support it gives to the UK's armed forces.
It concludes that investing more in defence would be good for the economy as a whole.
BBC defence correspondent Caroline Wyatt said the reports, coming ahead of the party conference season, represent the UK defence industry firing a warning shot in advance of a period it fears will bring major cutbacks to defence spending.
It fears this would have serious consequences for one of Britain's biggest industries.
Our correspondent said the UK still punches above its weight in exporting defence equipment and technology, with the sector's investment in research and development also benefiting other sectors.
However, the defence industry remains heavily dependent on government spending, with around three-quarters of its turnover reliant on the MoD.
The ministry has come under increasing internal and external criticism over wasteful procurement procedures and the level of equipment available for troops in Afghanistan.
Mike Turner, chairman of the Defence Industries Council, said investment in the industry would help balance the economy and protect the country against security threats.
"As the economic frailties of the economy become more apparent, there has perhaps never been a better opportunity to harness the full potential of our world-class defence and security industrial base and use it as one of the paths out of recession," he said.
"We are determined to highlight the benefits the industry delivers to the UK and its armed forces. We believe that, contrary to the prevailing mood in Westminster, now is the time to consider investing more for our future safety, not less."