LOS ANGELES (Reuters) - U.S. nonprofit Climate United on Tuesday announced a plan to spend up to $250 million to buy as many as 500 electric semi trucks over three years in what it called the biggest single order of those zero-emissions trucks in the country so far.

Climate United then aims to lease those vehicles at attractive rates to truckers that haul containers to and from California seaports, where roughly 33,000 so-called drayage trucks must have zero tailpipe emissions by 2035.

The program could give a much-needed jolt to the adoption of heavy-duty electric trucks that now account for less than 1% of the total U.S. trucking fleet. Those vehicles can cost as much as three times more than traditional diesel versions that are a major source of planet-warming greenhouse gases.

"High upfront costs make it difficult for independent owner-operators and small fleets to transition to all-electric," said Beth Bafford, CEO of Climate United.

The Maryland-based nonprofit said it plans to make initial orders in the first quarter of 2025 and that it is prioritizing class 8 trucks that are assembled in the United States with domestically made parts.

Trucks from manufacturers like Volvo Trucks North America, BYD and Kenworth already are shuttling cargo around ports in California, including the nation's busiest seaport complex in Los Angeles and Long Beach.

Climate United's program is funded by a $6.97 billion grant from the National Clean Investment Fund, part of the Greenhouse Gas Reduction Fund created under President Joe Biden's Inflation Reduction Act.

Climate United also is partnering with Forum Mobility, which is building charging depots in California ports and along common freight routes.

"For so long, this has been the story of the chicken and the egg. You can't have the trucks before you have the charging, and you can't have the charging before you have the trucks," said Jacqueline Torres, a vice president at Forum Mobility.

"This program brings both of those together."