Conspicuous consumption has never come easy to William H. Gates, the chairman and chief executive of the Microsoft Corporation. But these days the mantle of world's richest man seems to be resting easier on his shoulders. Earlier this month, Mr. Gates broke down and bought himself a $21 million private jet.

For years, even as his wealth ballooned to its current level near $40 billion, Mr. Gates was known for flying coach. His preference on long trips was to throw a blanket over his head and sleep.

Microsoft employees are still restricted from flying first class and can upgrade to business class only on international flights. That is apparently why Mr. Gates, who will turn 42 tomorrow, bought the plane himself, rather than have Microsoft pay for it.

''He is flying so much it really does make sense, but he doesn't think the company should be paying for it,'' said Pam Edstrom, a spokeswoman.