By Doyinsola Oladipo and David Shepardson

NEW YORK/WASHINGTON (Reuters) -U.S. dock workers and port operators reached a tentative deal that will immediately end a crippling three-day strike that has shut down shipping on the U.S. East Coast and Gulf Coast, the two sides said Thursday.

The tentative agreement is for a wage hike of around 62% over six years, two sources familiar with the matter told Reuters, including a worker on the picket line who heard the announcement. That would raise average wages to about $63 an hour from $39 an hour over the life of the contract.

The International Longshoremen's Association (ILA) workers union had been seeking a 77% raise while the employer group - United States Maritime Alliance (USMX) - had previously raised its offer to a nearly 50% hike.

The deal ends the biggest work stoppage of its kind in nearly half a century, which blocked unloading of container ships from Maine to Texas and threatened shortages of everything from bananas to auto parts, triggering a backlog of anchored ships outside major ports.

The union and the port operators said in a statement that they would extend their master contract until Jan. 15, 2025 to return to the bargaining table to negotiate all outstanding issues.

"Effective immediately, all current job actions will cease and all work covered by the Master Contract will resume," the statement said.

Among key issues that remain unresolved is automation that workers say will lead to job losses.

Union boss Harold Daggett said previously that employers such as container ship operator Maersk and its APM Terminals North America had not agreed to demands to stop port automation projects that threaten jobs.

U.S. President Joe Biden’s administration had sided with the union, putting pressure on the port employers to raise their offer to secure a deal and citing the shipping industry's bumper profits since the COVID-19 pandemic.

The tentative deal "represents critical progress towards a strong contract," Biden said on Thursday. "Collective bargaining works," he added.

His administration has repeatedly resisted calls from business trade groups and Republican lawmakers to use federal powers to halt the strike - a move that would undermine Democratic support among unions ahead of the Nov. 5 presidential election.

The White House had been heavily involved in talks to get a deal, sources said.

After days of talks, White House Chief of Staff Jeff Zients convened a 5:30 a.m. (0930 GMT) virtual meeting on Thursday with the CEOs of ocean carriers and impressed upon them the need to reopen the ports to speed hurricane recovery efforts, according to a source briefed on the events.