* Long-dated Treasuries underperform short end

* Upcoming supply, technical selling weigh on long end

* Productivity gain argues for low inflation

* Short-end draws support from stable Fed outlook

By Ellen Freilich

NEW YORK, Nov 5 (Reuters) - Big gains in U.S. workers' productivity in the third quarter supported short-dated U.S. government securities prices on Thursday, while upcoming supply weighed on long-dated debt.

Meanwhile, data showing a drop in new U.S. claims for jobless benefits and the productivity gains, which promised better corporate profits, pushed stocks higher. That also depleted the bid for safe-haven U.S. government debt as investors showed a willingness to shoulder riskier assets.

"The third-quarter productivity gains would limit inflation concerns to some degree, which in this environment is probably more important for what it means for Federal Reserve policy, so it is helping to support the front end," said John Canavan, analyst at Stone & McCarthy Research Associates.

At the same time, "positioning before next week's refunding weighs on 10s and bonds especially heavily," he said.