E.I. du Pont de Nemous & Co., the nation's largest chemical company, today won the most expensive and one of the most bitter corporate takeover fights in American business history.

A champagne celebration was held at Du Pont headquarters in Delaware, but the victory had its price: Seagram Co. will end up as Du Pont's largest stockholder and many claim some of the chemical firm's assets in exchange for its current and prospective holdings.

What Du Pont won was a five-week, three-way struggle for Conoco Inc., the nation's ninth-biggest oil company and second-biggest coal company.

Du Pont bested Mobil Corp., the nation's second-largest oil company. Mobil's final $8.8 billion bid was richer than Du Pont's $7.6 billion cash and stock offer but Mobil's bid could not survive the taint of potential federal antitrust challenges.

Du Pont also thwarted Seagram's attempts to acquire 51 percent of Conoco. Du Pont has control of 55 percent of Conoco's 86 million shares and probably will pick up more before its offer to buy expires Aug. 17.

Du Pont also thwarted Seagram's attempts to acquire 51 percent of Conoco. Du Pont has control of 55 percent of Conoco's 86 million shares and probably will pick up more before its offer to buy expires Aug. 17.

But Seagram could end up a big winner. The Montreal-based distiller, which touched off the bidding war in late June, will become the biggest shareholder in the combined Conoco-Du Pont and might be able to force concessions from Du Pont. Wall Street sources said that Seagram might seek to exchange its Du Pont stock for Conoco's Consolidation Coal company and some natural gas operations.

The distiller already has bought at least 15.5 million hares of Conoco, at $92 a share, and Mobil announced this morning as its final shot in the takeover war that it would send the 735,000 shares of Conoco it owns to Seagram. Merrill Lynch & Co., Mobil's adviser in the fray, also owns, several hundred thousand shares of Conoco and will send them to Seagram. Under the Du Pont offer, each share Seagram owns of Conoco is worth 1.7 shares of Du Pont stock.

Most of the 38.7 million shares Du Pont was willing to pay $98 cash for have been bought, and Conoco shareholders who want cash rather than Du Pont securities worth about $77 were offering their stock to Seagram today.

Seagram already is assured of controlling 12 percent of Du Pont stock, and its holdings could go as high as 20 to 25 percent. Conoco was the most active issue on the New York Stock Exchange today as professional traders bought the stock for slightly less than $92 a share and then sold shares to Seagram. Investors also boosted Du Pont's shares by $1.75 to $46.875.

Seagram also announced late today that it will extend its offer to purchase Conoco stock from midnight tonight until midnight Friday.

If Seargram ends up with 20 percent or more of Du Pont stock, it could demand representation on the other company's board and a role in its corporate decisions. Whether or not Du Pont agreed to such a request, Seagram's interests could be expected to clash with those of Du Pont management

Du Pont's victory was clinched at midnight Tuesday, when the so-called withdrawal period in its offer expired. After midnight, Conoco shareholders who had shipped their stock to Du Pont could not take it back. By then Du Pont had 47.3 million shares in hand -- a firm 55 percent and more than enough to control Conoco. At 3:45 a.m. today Du Pont began paying $98 a share for 37.9 million shares that demanded cash payment. Each of the remaining 9.4 million shares will be exchanged for 1.7 shares of Du Pont.

At midnight Du Pont Chairman Edward Jefferson hosted a champagne party for the 200 or so Du Pont employes who have spent the last month working nearly round-the-clock on the takeover. "There was some jubilation. But we were all bone tired. The party lasted about an hour. We weren't the typical kick-up-your-heels crowd," said a Du Pont official who attended.

Du Pont was Conoco's pick to win the bidding war. Seagram, cash-rich after selling its U.S. oil properties to Sun Oil Co. last year, made an unfriendly after for Conoco at $73 a share in late June after Conoco's board of directors rebuffed a friendly bid.

Conoco Chairman Ralph Bailey and Du Pont's Jefferson then began negotiating for a friendly Du Pont bid. On July 6 Du Pont made its first offer of $87.50 a share for 34.44 million shares and 1.6 shares of Du Pont for each of the remaining Conoco shares. Du Pont stock was then trading at about $51 a share (compared with about $47 today) and the offer was worth $7.3 billion. Du Pont, whose petrochemical operations were hit hard during the 1974 Arab oil embargo, looked with glee at Conoco's extensive oil reserves.

Mobil launched its attack July 17, offering $7.74 billion, and touched off a month-long series of frenzied bidding that ended Tuesday. At the end Mobil was offering $120 a share in cash for half the stock and securities worth $85 a share for the rest, a total of $8.8 billion. Du Pont was offering $98 a share for 45 percent of the stock, while Seagram's final offer totaled $4.08 billion.

The companies spent as much time in court as in strategy sessions. Conoco convinced county courts in Florida and in North Carolina to block Seagram's offer on the grounds that a Seagram takeover of Conoco would violate state liquor laws. Both orders were overturned, and Seagram began writing checks about 1:30 p.m. last Saturday, about 13 hours later than planned.

Mobil tried to block Du Pont from ending its withdrawal period on Tuesday, but could convince neither a U.S. District Court judge nor an Appeals Court judge to issue the necessary orders.

Conoco sued to stop the Mobil bid on antitrust grounds but in the end the Justice Department assured the outcome. By clearing Du Pont and extending its investigation of Mobil's bid, the government spurred investors to ship their stock to Du Pont in sufficient quantities.