- The 22 unarmed drones reportedly worth more than $2 billion
- Indian navy is getting drones to keep watch over the Indian Ocean
- India, US will also discuss sale of US fighter jets during PM Modi's trip
The report added that the deal has been approved by the US State Department and has been communicated to the Indian government and the manufacturer of the drone, California-based General Atomics.
Securing agreement on the purchase of the 22 unarmed drones - reportedly worth more than $2 billion - was seen in Delhi as a key test of defence ties that flourished under former President Barack Obama but drifted under Mr Trump, who has courted India's rival China as he seeks Beijing's help to contain North Korea's nuclear programme.
PM Modi's two-day visit to Washington begins on Sunday. Mr Trump met Chinese President Xi Jinping in April and has also had face-time with the leaders of nations including Japan, Britain and Vietnam since taking office in January, prompting anxiety in Delhi that India is no longer a priority in Washington.
The Indian navy getting the unarmed surveillance drones it wants to keep watch over the Indian Ocean will be the first such purchase by a country that is not a member of the NATO alliance.
"We are trying to move it to the top of the agenda as a deliverable, this is something that can happen before all the other items," said one official tracking the progress of the drone discussions in the run-up to the visit.
India, a big buyer of US arms recently named by Washington as a major defence ally, wants to protect its 7,500 km (4,700 mile) coastline as Beijing expands its maritime trade routes and Chinese submarines increasingly lurk in regional waters.
But sources tracking the discussions say the US State Department has been concerned about the potential destabilising impact of introducing high-tech drones at a time when tensions are simmering between India and Pakistan.
"There is a palpable fear in New Delhi that the new US president's lack of focus on India, and limited appointment of South Asia focused advisors, has resulted in India falling off the radar in Washington," Eurasia Group's Shailesh Kumar and Sasha Riser-Kositsky said in a note quoted by news agency Reuters.
Defence deals, however, are one area where the two countries could make progress.
The two sides had stepped up efforts in recent weeks to get inter-agency clearance for the sale of the Guardian drone.
India has raised the issue of the drones with the Pentagon three times since June 2016, officials said, according to Reuters. The agency also said that an industry official involved in promoting India-US business ties said the drone sale enjoyed support from the White House and Congress.
While the Guardian drones that India is pushing for are unarmed, the Indian military had originally asked for missile-firing Predator Avenger aircraft, a request turned down by the Obama administration.
US export laws typically prohibit the transfer of such arms to a country unless it is fighting alongside US forces.
India and the United States will also discuss the sale of US fighter jets during PM Modi's trip, in what could be the biggest deal since they began deepening defence ties more than a decade ago.
On Monday, Lockheed Martin announced an agreement with India's Tata Advanced Systems to produce F-16 planes in India, provided it won a contract to equip the Indian Air Force with hundreds of new aircraft.
Lockheed has offered to shift its ageing F-16 production line from Fort Worth, Texas as part of PM Modi's "Make-in-India" drive while it ramps up production of the high-end F-35 aircraft at home.
Since Mr Trump's election on an "America First" platform, US and Indian officials have sought to play down any contradiction between his stated desire to protect American jobs and PM Modi's "Make in India" policy, arguing, for example, that deals in which components made in the United States are shipped to India for assembly benefit workers in both countries.
US officials expect a relatively low-key visit by PM Modi, without the fanfare of some of his previous trips to the United States, and one geared to giving the Indian leader the chance to get to know Mr Trump personally.
PM Modi is expected to discuss the H 1-B visa programme that the Trump administration is reviewing to reduce the flow of skilled foreign workers and save jobs for Americans.
Indian Trade Secretary Rita Teaotia told reporters this week that the H-1B visas, under which Indian IT firms send large numbers of professionals to the United States, would be one of the issues on the table during PM Modi's visit.
With inputs from Reuters and PTI