A union local at Bethlehem Steel's ailing Sparrows Point shipyard today approved by a 10-to-1 margin a no-strike provision aimed at luring a big Navy contract, a union official said.

James Harmon, executive secretary of Local 33 of the Industrial Union of Marine and Shipbuilding Workers of America, said the no-strike provision would extend until August 1985, the expected completion date for a Navy contract worth millions of dollars and an estimated 2,000 jobs.

Harmon had recommended approval of the provision, which he called necessary, although he said "it goes against my grain as a union official."

"I've got 2,800 people out of work and at this time to get work we have been informed by sources that delivery dates are the most important parts of the bids," Harmon said.

The program, known by the Navy as T-AKX, involves conversion of five commercial ships for use by the Navy's Rapid Deployment Force. Local 33's information sheet said the Navy was "requesting that the union agree not to strike while the T-AKX program is being built in our yard."

Cdr. R.L.Gustavus, the Navy contracting officer responsible for the program, declined to comment on what was in the bid requests.

The workers' current agreement expires in August 1984. Under the agreement approved tonight, they would remain on the job under the current contract until the final Navy vessel is completed the following year.