WASHINGTON. March 21 (Reuters) - The United States plans to speed up the delivery of Abrams tanks to Ukraine, a Pentagon official said on Tuesday (Mar 21), providing the vital equipment to Kyiv as soon as this fall to defend itself against Russian forces.

In January, the US pledged to supply Ukraine with 31 advanced M1A2 Abrams tanks after months of shunning the idea of deploying the difficult-to-maintain tanks to Ukraine, which was invaded by Russia in February 2022.

US officials and a source familiar with the situation earlier told Reuters about the change in timing of delivery.

The new plan would give Ukraine the M1A1 SA Abrams tank variant, which can run on diesel fuel like the majority of the Ukrainian fleet, one of the officials said. The change also speeds up delivery by about a year, according to a congressional aide briefed on the matter.

The Pentagon "in close coordination with Ukraine has made the decision to provide the M1A1 variant of the Abrams tank which will enable us to significantly expedite delivery timelines and deliver this important capability to Ukraine by the fall of this year", Pentagon spokesperson Brigadier General Patrick Ryder told reporters.

The Department of Defense had not previously offered any specific date to get the tanks into Ukrainian hands, only saying it would take "months". On Tuesday, Ryder offered that the previous timeline had been in excess of a year.

US Defense Secretary Lloyd Austin looked at several options for quickening the delivery, the congressional aide briefed on the plan told Reuters.

Examples of options Austin could have evaluated included changing positions in the delivery queue, or using US tanks that have had their sensitive equipment removed, so that it cannot be captured and studied by Russian troops.

The General Dynamics Corp production line is currently completing about 12 Abrams tanks a month. The M1A2 tanks would be sourced from government-owned "hulls" and refurbished specifically for Ukraine, Ryder said.

Funds to alter or buy Abrams tanks would come from a fund known as the Ukraine Security Assistance Initiative (USAI), which allows President Joe Biden's administration to get weapons from industry rather than draw from US weapons stocks.

The Pentagon earmarked US$400 million worth of USAI funds in January for the initially planned 31 M1A2 tanks. Those same dollars would be put to use in creating this batch of M1A1s, Ryder said.