WASHINGTON, May 5 - Washington is working to push through contracts for tens of billions of dollars in arms sales to Saudi Arabia, some new, others in the pipeline, ahead of US President Donald Trump's trip to the kingdom this month, people familiar with the talks told Reuters this week.Saudi Arabia is Trump's first stop on his maiden international trip, a sign of his intent to reinforce ties with a top regional ally.The United States has been the main supplier for most Saudi military needs, from F-15 fighter jets to command and control systems worth tens of billions of dollars in recent years. Trump has vowed to stimulate the US economy by boosting manufacturing jobs.Washington and Riyadh are eager to improve relations strained under President Barack Obama in part because of his championing of a nuclear deal with Saudi foe Iran.