The Supreme Court yesterday refused to overturn a ruling giving organizers for the Amalgamated Clothing and Textile Workers the right to try to organize inside nonunion plants operated by J.P. Stevens & Co.

On any other day in the historically stormy relationship between the union and the nation's second-largest textile manufacturer, the court's decision would have been greeted as a labor victory.

But, ironically, the decision -- actually a decision without comment to leave intact a National Labor Relations Board order on the matter -- came the day after ACTWU signed its first contact with Stevens, ending a bitter, 17-year battle with the firm.

In the contract, the union agreed to suspend for 18 months the very practices that the court, in effect, said it had the right to use -- posting notices on plant bulletin boards, talking to employes in plant restaurants and in other nonwork areas like parking lots and conducting related organizing activities inside the plant or on plant grounds.

Spokesmen for Stevens, which has been trying to put the best face on its decision to sign a union contract covering 10 of its 80 plants, yesterday pointed with ill-concealed glee to what they called a "major concession."

"They gave up a hell of a lot," said one Stevens spokesman commenting on the ACTWU contract. He said the union's ageement to suspend some of its organizing rights proves that the company "got a hell of a lot more than we gave."

However, ACTWU officials were not to be outdone in the image battle.

"The Supreme Court ruling affirms the right of the union to have access. It doesn't order us to have access," said ACTWU spokesman Burt Beck. The union didn't have that right through much of its dealings with Stevens, Beck said.

Besides, he added, "If we want to voluntarily give up something, we may do so. But we didn't give up those rights; we exchanged them for something else," Beck said.

That "something else" is called "portability" -- which means that Stevens agreed that the contract it signed Sunday with ACTWU will be applicable, to a greater or lesser degree depending on "local conditions," to other plants the union manages to organize, the union claimed.

This newest development in the labor battle that has spawned two books, a movie and incalculable inches of newspaper print, stems from an NLRB order issued in response to federal labor law violations committed by Stevens in 1976.

The board then found the company guilty of forcing employes at its Tifton, Ga., plant to answer questions about ACTWU organizing activities and of threatening to discipline workers who talked to union organizers.

As part of a series of "extraordinary remedies," the board ordered Stevens to honor the union's reasonable requests for access to bulletin boards and nonwork spaces to sell its position. That order was upheld last Jan. 8 by the 4th U.S. Circuit Court of Appeals.