BOSTON — A combination of Microsoft and Yahoo could reshape the Internet landscape for millions of Web users: Would the two companies join their online portals? Could they rethink the desktop computer to integrate Web content more directly?

The changes are potentially huge, but probably not in the short term.

Microsoft executives did not indicate yesterday exactly what they would do with Yahoo's brand if their bid, now valued at $42 billion, is accepted. But analysts expect the combined companies to preserve many of their separate free services, like instant-messaging and e-mail programs.

A more likely medium-term change is that some of Microsoft's Web content could fade away or get added to Yahoo, which has a vast collection of news and features aggregated from other providers.

Microsoft's Web properties, including its Yahoo-like MSN portal, aren't exactly slouches: They rank third, trailing only Yahoo and Google, in total visitors. But while Yahoo still is profitable, Microsoft's online services are a consistent money loser. The MSN search engine is a laggard, even with recent efforts to soup it up under Microsoft's online umbrella it calls "Live."

MIXING WEB, COMPUTING

Having Yahoo in its tent could give Microsoft a rationalization for abandoning its unprofitable online elements.

"I think MSN folds into Yahoo," said Ian Campbell, CEO of Nucleus Research. "It would be foolish to keep that separate."

Perhaps the biggest change Microsoft and Yahoo could achieve together would be creating a better way to combine the Web and desktop computing — not to mention cell phones, TVs, cars and any other gadgets that might someday plug into the Internet.

Consumers who access the Web on cell phones and handheld computers might be the first to find something new as a result of a Microsoft-Yahoo combination. Devices that run Microsoft's Windows Mobile operating system could be better integrated with Yahoo content and possibly yield new services, like social networking functions.

New ideas will be key to compete with Google's Web presence. After all, people don't "Microsoft" or "Yahoo" anything. Microsoft in particular tends to be tolerated more than loved. Google is also leading development of an alternative cell-phone operating system it calls Android.

Eventually, a teamed-up Yahoo and Microsoft might be able to rethink the PC desktop — where Windows still runs 90 percent of the world's PCs — so that Internet data such as stock prices, sports scores and weather are automatically baked in.

"We all have our home page because we have a concept of a home page," Campbell said. Before long, "we may not have a home page — it might just be the background of my desktop. There's no reason why Microsoft can't push this another level."

EXPLOITING STRENGTHS

Microsoft might also use Yahoo's online strengths to galvanize Web-based versions of some of its powerful desktop software applications, like Word and Excel.

Open-source rivals and Google are threatening to bite into Microsoft's lucrative Office software franchise with free versions of those kinds of "productivity" software. Microsoft is developing Web-based versions of its own, but slowly.

Now Yahoo could be the face through which Microsoft offers those online applications. Perhaps one day a Microsoft-fueled package of "Yahoo Apps" will go up against "Google Apps."

Even with these possibilities, analyst David Mitchell Smith, a vice president at Gartner Inc., believes the biggest change from a Microsoft-Yahoo deal probably will be the one most Web surfers don't notice. That will come as the companies try to broaden their ability to deliver ads all over the Internet, wherever it reaches.

It's necessary because being the most popular online destination — as Yahoo already is — is no longer enough.

The explosion of blogs, video sites and other user-generated content has made our Internet travels more wide-ranging. As a result, the biggest Internet companies now need their ad networks to reach far beyond their home portals. Google has mastered that. Microsoft and Yahoo have not.

"I think that's really what it's all about," Smith said. "It's about advertising. It's about search."