Microsoft lawyers yesterday grilled the top executive of rival software group, Netscape, for a third day at a landmark antitrust trial in a bid to show Microsoft's business strategy had never been dictated by Netscape.

Microsoft attorney, Mr John Warden, questioned Mr James Barksdale, Netscape's top executive and the key government witness, trying to show that the company had not tried to harm Netscape and snuff out competition in the software industry.

The US Justice Department has accused Microsoft of illegally trying to extend its monopoly of the operating systems market for personal computers into other Internet-related domains, notably the browser sector.

The antitrust trial, likely to change the face of the US software industry, was in its fourth day before US District Court Judge, Mr Thomas Penfield Jackson.

Working with a written text of Mr Barksdale's pre-trial testimony, Mr Warden sought to show that Netscape had always planned to give away its browser, known as Navigator, and had focused its strategy on other software products as well as on the market for servers.

He showed the court a document, dated November 1994, in which Netscape co-founder, Mr Mark Andreessen, wrote that the company was "absolutely committed to giving away 1.0 for personal use," referring to the first version of Navigator.

"Mark Andreessen was speaking for himself and not the corporation," Mr Barksdale insisted.

The line of questioning was to show that Netscape intended to distribute Navigator for free well before Microsoft came to the same decision.

Microsoft also maintains that it had long planned to incorporate its own browser, Explorer, in Windows 98, the latest version of an operating system now in use in 90 per cent of personal computers worldwide.

The browser was not built into the previous version, Windows 95, and the government contends that integrating browsing technology in Windows 98 was designed to damage sales prospects for Netscape Navigator.

Mr Warden asked Mr Barksdale if he were convinced that Microsoft could separate Explorer from Windows 98.

It could be done, the witness replied, "if Microsoft chooses to do so." He added that given the dominance of the Windows system Netscape was obliged to write software compatible with it.

Microsoft has argued that the browser and Windows 98 constituted an integrated product and that to separate them would impede the operating system.

But Mr Barksdale contended that if Microsoft were able to provide separate versions of its browser to Apple Computer, it should be able to do so for other computer makers.

The trial is due to resume on Monday.