The American internet search group said that the deal would bolster distribution of Sun’s OpenOffice software, which offers similar programs to those available on Microsoft Office, such as word-processing software.

Microsoft Office is the world’s dominant office software program but its Word, Excel and Powerpoint programs compete head-on with OpenOffice equivalents.

Scott McNealy, Sun’s chief executive, said: “Working with Google will make our technologies available more broadly, increase options for users, lower barriers and expand participation worldwide.”

The two companies said that they had agreed to “explore opportunities” to promote Sun products. However, Eric Schmidt, Google’s chief executive, said that beyond agreeing to work together, no firm plans had been made.

The agreement will also see Google promote Sun’s Java software, which is required to run many internet applications.

Although the Sun products covered by the agreement are already available — and free to the user — the move will undermine Microsoft’s dominance. Analysts said last night that the arrangement would give Sun prominent exposure on Google’s internet home pages, which have more than 80 million unique users each month.

Users of Sun’s software will also be given the option to download Google’s Toolbar, a panel that sits on the user’s internet browser, such as Internet Explorer. The Toolbar blocks pop-up adverts and offers an instant search facility without the need to open a new window.

Dr Schmidt said that growth in the use of the Toolbar would benefit Google because it tended to promote greater and more sophisticated use of the search engine, a great attraction for advertisers.

Bill Gates, the head of Microsoft, conceded in May that Google was “more like us than anyone we have ever competed with”. Last month Kai Fu Lee, a former Microsoft executive, faced his former employer in a Seattle pre-trial hearing, in a battle over his attempt to jump ship to join Google. Microsoft said that Mr Lee was in breach of his employment agreement by leaving to work for a rival.

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