CLAIRTON, Pa. (AP) _ The last time Tony Alfonsi carried a picket sign was 27 years ago during a nationwide steel strike that lasted 116 days. This time, he and his buddies say, it may be longer.

''I never dreamed I'd be back on a picket line,'' the 57-year-old steelworker said last week as he stood outside the gates of USX Corp.'s Clairton Works.

''It's a shame it's come to this. I figured the company and the union would have got together on something, especially the way it is today,'' he said.

The work stoppage involving 22,000 active workers at USX, formerly U.S. Steel, began Aug. 1. The company calls it a strike; the United Steelworkers union has labeled it a lockout. No new talks are scheduled.

Union officials say about 10 percent of those off the job at USX are veterans of the 1959 strike, th longest in steel history. The walkout was against 11 companies that produced 90 percent of the nation's steel, and it took a Supreme Court injunction to get the 500,000 strikers back to work.

''Everything was booming back then,'' said Alfonsi, a millwright and 37- year employee at Clairton.

''In '59, you knew someplace down the line, they were going to settle. There was no doubt about you coming back to work. This time, you don't know where you're at. The company may decide to shut her down. They're holding you hostage,'' he said.

USX wants reductions in labor costs of about $3 an hour, including a $1.25 wage cut, plus changes in work rules. The company is also threatening to shut down unprofitable plants.

The USW, which once boasted it had the best-paid industrial workers in the world, is trying to hold the line against concessions. USX rejected the union's proposal to freeze wages and eliminate a week's vacation and three paid holidays in exchange for job security.

Alfonsi's house and car are paid for and his two daughters have their college degrees. But ''anytime you step out like this, you're risking everything,'' he said.

''Why am I doing it? It's either cut and run, let them dictate to you, or fight and say I'm a human being and I'm trying to make a decent living.''

USX makes an estimated 17 percent of the nation's steel. The industry is expected to ship about 54 percent of the steel it is capable of producing, which means other steelmakers can meet market needs.

Largely because of that overcapacity and its causes - sluggish demand, cheap imported steel and resulting low prices - the eight largest steelmakers have lost $8 billion since 1982. Two have filed for bankruptcy protection.

Given the woeful state of the industry, Alfonsi and his co-workers expect a bitter, protracted battle.

Pete Worhatch and 30 of his friends in an electrical maintenance gang threw an impromptu Christmas party when they met July 28 to talk pre-strike strategy.

''We had coffee and doughnuts. ... Everyone said Merry Christmas. We figured we were going to be out at least that long,'' said Worhatch, 52, who has worked at Clairton for 29 years.

The Clairton mill makes coke from coal for the company's steel operations and converts chemical byproducts into road tar, fertilizer, perfume, nylon stockings and embalming fluid.

The work stoppage has had little effect on them so far, the workers say. They are still owed some pay, but unlike 1959, the union has a strike fund totaling $210 million. Workers are eligible for $60 a week in strike benefits after the third week. And if the courts rule the stoppage is a lockout, they could qualify for unemployment benefits of $150 to $300 per week.

There are ways to get through even a long strike, oldtimers say.

''You worked for your in-laws or your parents, just to get a meal. ... You have to scratch a little bit. Bounce and scrounge,'' said Al Kerr, 52. ''We'll hang in there. We did it before.''