Modi (1)
Indian Prime Minister Narendra Modi speaks during the launch of the Jan Dhan Yojana, or the Scheme for People's Wealth, in New Delhi August 28, 2014. REUTERS/Adnan Abidi

(Reuters) - The United States said on Wednesday it will press India's new prime minister to end his blockage of a global trade pact when he visits Washington this month, something that could dampen the mood of a trip aimed at revitalizing strategic ties.

U.S. Assistant Secretary of State Nisha Biswal said India "does itself a discredit" by blocking the Trade Facilitation Agreement (TFA) reached in Bali last year, rekindling a dispute that overshadowed an Aug. 1 meeting between U.S. Secretary of State John Kerry and Indian Prime Minister Narendra Modi in New Delhi.

In a conference call previewing Modi's Sept. 29-30 visit to Washington for a first meeting with President Barack Obama, Biswal said the World Trade Organization agreement to ease worldwide customs rules would "certainly" be a topic for conversation.

"We've made our position very clear, which is that while we are very sympathetic to the food-security concerns the prime minister has voiced, we do believe that the trade facilitation agreement is a very, very important agreement," she said.

In late July, India torpedoed the deal after demanding concessions on agricultural stockpiling.

Biswal said the stance "undermines India's interests as well as the interests of ... many developing countries and emerging economies.

The top U.S. naval officer, Admiral Jonathan Greenert, meanwhile, expressed hopes of expanding a security relationship with India that has failed so far to live up to Obama's billing as "one of the defining partnerships of the 21st Century."

Greenert told reporters on Wednesday at a military conference he was hoping for "clarity" on U.S. military sales and cooperation with India when Modi visits.

"Some of our cooperative measures in that regard have sort of stalled," he said at the Naval War College in Newport, Rhode Island.

Greenert said the United States was keen to ramp up joint exercises to again include carrier and submarine operations. "We haven't done that in a little while," he said. "I'd like to get back on that track."

In spite of enthusiastic U.S. rhetoric about Modi's visit, it remains unclear what it will achieve.

A key aim will be to clear the air. Before Modi became prime minister he was barred from visiting the United States after Hindu mobs killed more than 1,000 people, most of them Muslims, in 2002 while he was chief minister of his home state of Gujarat.

Biswal has played down expectations of quick progress on bilateral issues, not least when it comes to opening up India's civilian nuclear sector to U.S. firms, which is hindered by their concerns about India's liability laws.

She said there were still "tough issues to be worked through" on the nuclear issue.