A strike here has idled Maremont Corp., the nation's only manufacturer of machine guns and a major supplier of military hardware and auto parts.

The 850 members of the Amalgamated Clothing and Textile Workers walked out when three months of bargaining failed to reach an agreement. Despite a week of talks with federal mediators, union and company officials say the two sides are still far apart on wages, insurance, pension plans and other issues.

Maremont is under contract with the Defense Department to build the 50-caliber M-2 machine gun. The firm was awarded $13 million last July to build a few of the guns, but Maremont officials say the contract could total $100 million over the next five years.

Paul Scholfield, industrial relations manager for Maremont New England, says, "The company is offering a 29 percent increase, that's including pay and fringe benefits over the next three years." He says workers at the plant earn an average hourly wage, "including incentive pay for piece work" of $4.52.

The union's chief negotiator, Denis Blais, says Maremont has unfairly compared wages with those earned by local textile workers. Blais says Maremont workers should earn wages comparable to Portland area machine shop and tool workers.

The company and union reportedly are separated by 35 cents per hour for the first contract year and 25 cents during the second year. Maremont is seeking a third year for the contract but the union is not.

A spokesman for the U.S. Army Armament Readiness Command says most of the M-2s Maremont makes "are for foreign sale. They build many different kinds of weapon parts as well as machine guns. The strike shouldn't be a big problem." He had to comment on the Army's position on delayed delivery of weapons. Maremont continues to build parts for the Vietnam-war-era M-60 machine gun.

Maremont's Scholfield adds, "The government would consider a strike a reasonable explanation for delayed production and failure to meet contracts."

Union negotiator Blais adds, "They won't give us a cost-of-living clause. They want long-term contracts so they can do planning for bids, but we can't count on cost-of-living increases."

He says the union settled on a three-year contract during the last negotiating session. "We got stuck with a three-year contract and we just never caught up. We had only a 5 percent annual increase. Our people don't want that to happen again. Even with a two-year contract we want a cost-of-living increase."

Maremont is the area's largest manufacturer employing about 1,000. Besides weaponry, the company makes a line of auto parts ranging from mufflers and shock absorbers to alternators.

The company holds contracts to produce exhaust systems for a Volkswagon, MacPhersen struts and alternators, original equipment shock absorbers for Ford Motor Co., and private label auto parts for J.C. Penney and Sears. Maremont's sales totaled more than $250 million in 1977.