NEW YORK, NOV. 21 -- Triangle Industries Inc., the world's largest consumer packaging and container producer, said today that it had accepted an unsolicited $1.3 billion takeover offer from the state-owned French conglomerate Pechiney SA in a deal that will allow Triangle's top management to buy back its nonpackaging operations.

The acquisition would make Pechiney by far the largest company in the field, and comes at a key time as it prepares for the unification of the Western European market in 1992.

The deal requires regulatory approval.

Triangle stock soared $35.78 1/2 a share to close at $46.25 in over-the-counter trading.

Triangle acquired National Can Corp. in 1985 and American Can Co.'s packaging business a year later, all primarily financed through high-yield, low-rated "junk" bonds underwritten by Drexel Burnham Lambert Inc. It makes metal, glass and plastic containers and packing products through its American National Can operations.

Pechiney, based in Paris, is a diversified industrial group with operations that include metals production and aerospace equipment.

Both companies valued the agreement at $1.26 billion, but the price actually is higher when Triangle's debt is included. Pechiney, in essence, agreed to assume Triangle's outstanding debt, which includes $2.6 billion in long-term securities.

Only 37 percent of Triangle's common stock is traded publicly. Chairman Nelson Peltz and President Peter W. May control about 63 percent of the common shares, and have 89 percent of the total voting power. The company was taken semi-private last summer.

For Peltz and May, the cash deal provides a capital windfall while allowing them to concentrate on Triangle's noncontainer and packaging operations, which include the production of juke boxes and vending machines and wire and cable. Pechiney said it would sell back those businesses to the executives for $225 million.

In a statement, Pechiney Chairman Jean Gandois said the company planned to make no major changes in management and strategic operations at Triangle's American National Can.

Under the agreement, Pechiney -- through its U.S. subsidiary, Pechiney Corp. -- would pay $56 in cash for each of Triangle's common shares and $101.02 a share in cash for each of the company's $2 preferred stock, which is convertible to 1.82 common shares.

In addition, Triangle's 15 3/4 percent preferred stock would be redeemed at $10.62 1/2 a share plus accrued dividends.