In taking over Conoco Inc. for the equivalent of more than $7 billion in cash and stock, E.I. du Pont de Nemours & Co. may not be the mouse that swallowed the whale. But it will at least be the chemicals tiger that ate the oil elephant.

Conoco, the nation's ninth-largest oil company, has more assets, a third again more sales revenue, and earnings that area almost half again higher than those of its acquirer. And about all the two companies share is their huge size and the production of certain petroleum-based chemicals.

The oil giant, based in Stamford, Conn., had 1980 sales of $18.8 billion, making it the nation's 14th-largest industrial corporation. Earnings reached $1.03 billion for a pershare figure of $9.52. And it assets, mostly in holdings of oil and coal refinery capacity, total slightly more than $11 billion.

As one might expect, oil is Conoco's principal business. Excluding Hudson's Bay Oil and Gas Co. Ltd., which Conoco sold to Canada's Dome Petroleum Ltd. earlier this year, oil and gas revenues accounted for 1980 totaled $15.9 billion, or 85 percent of sales. The petroleum operation also brought in 78 percent of earnings.

Worldwide, Conoco has more than 70 million net undeveloped acres of oil and gas leases, giving it the promise of fulfilling Du Pont's needs for chemical feedstocks for a long time to come. But one reason for Du Pont's lucrative takeover bid -- $87.50 a share for cash purchases and more than $70 a share for Conoco common bought with Du Pont shares -- is that Conoco owns Consolidation Coal Co., the nation's second-largest coal producer. Last year, the profitable Consolidation mined 44.9 million tons of coal, contributing 7.9 percent of revenues and 10.2 percent of net income. Sweetening the pot are coal reserves that one stock market analyst characterized as "awesome." According to Conoco's annual report, its currently recoverable coal reserves amount to 14.3 billion tons.

Chemicals production is the only area of possible overlap with Du Pont's operations. Conoco last year produced 2.05 billion pounds of basic industrial chemicals, ranging from ethylene to polyvinyl chloride resins to alcohols, and chemicals, contributed 5 1/2 percent of revenues and 4.3 percent of earnings.

Most market watchers agree that Du Pont's offer would be attractive to Conoco shareholders. The new merger agreement, sanctioned by conoco's management, comes in response to a $73 a share takeover bid by Canadian distiller Joseph E. Seagram & Sons.