An electronics trade show without the biggest names in the industry is sort of like a concert without the headline act.

That’s the problem facing the organizers of the International Consumer Electronics Show, which is scheduled to begin Tuesday.

More than 2,700 companies and 150,000 visitors are expected at the annual electronics show-and-tell event, but many household names won’t be among them. Instead, the exhibition floor of the world’s largest tech trade convention will be filled with smaller and mid-size companies promoting smartphones, tablet computers, Web-connected televisions and razor-thin laptops that mimic or build on hit products produced by the leading tech firms.

Apple as usual won’t be at the event, but the company’s iPad and iPhone products have spawned hundreds of companies that will be hawking things such as slipcovers and ear buds at the “iLounge” exhibit. Facebook also won’t be attending, but a slew of other social-networking companies will be showing off their newest offerings.

In December, Microsoft became the latest tech giant to bow out of the show, announcing this year’s appearance would be its last.

The show is still essential for companies such as Intel, which has bet big this year on ultrabooks — which it hopes will compete against Apple’s popular MacBook Air. It announced its microprocessors would be in 75 new ultrabooks — many below $1,000 — that will be unveiled this week and later this year by companies including Acer, Hewlett-Packard and Lenovo.

But the absence of Apple and Facebook, along with Google and Amazon barely registering here, highlights a fundamental shift in how products are launched and promoted in today’s high-tech industry.

Many of the products with the most buzz in 2011 — including Microsoft’s Kinect, Apple’s iPad 2 and iPhone 4s, Amazon’s Kindle Fire, Barnes & Noble’s Nook Tablet — were all unveiled at their own, gadget-specific events rather than at CES or other industry conventions.

“It used to be that CES was the center of the universe,” said Jeff Kagan, an independent analyst who as of last week was still deciding whether he should attend. “The popularity of these events come and go in waves, but it does feel like the real centers of the universe in tech are no longer at CES.”

Part of the challenge facing CES is that companies that once came to the convention to network and brainstorm about ways to collaborate now find themselves competitors. Since the show was founded in 1967, firms that started with one or two narrowly defined businesses have morphed into massive Internet and technology conglomerates that are competing for eyeballs and dollars in similar ways.

Amazon, for example, isn’t just a retailer anymore; it also makes devices and sells digital videos and songs.

Search giant Google competes with wireless carriers for mobile payments and makes the Android software for phones and tablet computers. And it is using CES to promote a new Web-based TV service with partners LG, Sony, and Vizio — a product that could put it in competition with cable television.

Microsoft, once known for its desktop software, leads video gaming with its XBox. Chief executive Steve Ballmer on Monday introduced new models of the Windows Phone, which will compete with Apple and Google.

Organizers of CES say that despite the changes in the industry, the event remains as popular as ever with attendance expected to match the record high of last year, and companies have rented more space to display their goods.

The Consumer Electronics Association, the trade group that puts on the show, said it has responded to shifts in the high-tech sector by broadening the definition of consumer electronics. The year, organizers devoted floor space for Internet-connected cars and home appliances, such as refrigerators, as well as devices and software for health, parenting and education.

“As the largest tech show in the world, we don’t categorize companies or products like we used to,” said Jason Oxman, vice president of industry affairs for the association. “What we do instead is offer opportunities to participate in areas of the show called Tech Zones and let companies decide for themselves how they want to define themselves.”