SAN FRANCISCO  Each year, Oracle’s presence looms over this city for a week, during the company’s Open World customer conference. About 41,000 people arrived this week to discuss business software in fine detail and talk over beers. Stretches of downtown streets closed and gave way to makeshift tents housing coffee stands, bars, Lego play areas and candy buffets.

But Oracle’s annual takeover of San Francisco pales against its larger ambitions  to supply just about all the technology, software and hardware, that businesses might need. This sweeping agenda has rattled the nerves of customers, who fear that Oracle has its own best interests, not theirs, at heart. The worry is that instead of saving money, customers will end up paying more over the long term, and that Oracle, already known for its aggressive tactics, will use its strong position in software to gain even more leverage over a larger array of products.

Companies have long used Oracle’s software to keep track of their most prized information. For Oracle, this resulted in sales of $26.8 billion last year and hints of an annual revenue goal of $100 billion. Over the last five years, Oracle has acquired a staggering 66 companies, most of which were software makers that provided expertise in niche areas.

This year, it bought Sun Microsystems, a hardware maker, signaling its intention to dominate the data centers of businesses by controlling more of their technology purchases. It is a prospect that its traditional partners and, more important, its customers, find unnerving.