When the Workers' Commission seized the Lusalite plant here in the summer of 1975, the commission leader, Manuel da Cruz Pires, told the departing owner:

"If you come back, I will kill you."

Today, the owner, Manuel Abecassis is once again running his family business and turning its losses into profits. Da Cruz Pires is still an angry young man, still leader of the Workers' Commission. Nevertheless, at regular meetings with Abecassis or his deputy, da Cruz Pires sits quietly across the table.

The fate of Lusalite, one of the two biggest makers here of asbestos fiber cement, used in building, epitomizes the new mood in Portugal.

In the months following the coup of April, 1974, the left was riding high.At Lusalite, they consisted of about a score of militants in a work force of 700, ranging from the Communists leftward.

De Cruz Pires, a suspicious, bearded, one-armed moulder, describes himself only as "revolutionary left," meaning somewhere beyond the Communists.

After taking the plant, he hand his fellow commissioners multiplied commissions. There was one for production (which did not stop a slide in productivity); there was another for parents, another for the disabled and another for "political and cultural dynamism.

It was all lively stuff, "all the folklore of April 25," as one executive puts it today.

Wages went up brisky and now average $210 a month. So did dovertime and night shift pay, accident benefits, pensions, school subsidies and everything else.Nobody worried very much about the bills, and Lusalite, with sales of about $10 million, ran into the red in 1975, 1976 and 1977.

Last summer, Mario Soares' government began a cautious retreat. Abescassis, scion of an old and rich Portuguese Jewish family, was given back his plant by the industry minister, who had been trained at the Massachusetts Institute of Technology.

Today, things are far from idylic but better. Out put is 25 percent above the pre-coup level. Sales in real terms are expected to increase 14 percent this year. Lusalite is budgeting for a profit despite a wages and benefits bill that has tripled since the takeover.

Da Cruz Pires tries but cannot describe any "concrete" way in which the workers are worse off with Abecassis back. Nevertheless, he insists, "a boss is always negative, especially a family boss."

Da Cruz Pires complains that he can no longer see the books, that foremen are once again supervising wokers, that morale - if not pay - is lower. Nobody mentions his threat to kill the boss, and acknowledges that he and his fellow commissioners have not suffered any discrimination.

Revolutionary slogans are still painted on the factory's walls. But apart from that, Lusalite has the feel of a well-run, Western plant, that could make a solid contribution to Portugal's effort to pull itself out of an economic morass.