Mary Gates, 64, a director of major banking and communications corporations whose contacts greatly helped her son Bill's Microsoft Corp. Mrs. Gates was a director of several companies, including First Interstate Bancorp, US West Inc. and KIRO-TV, a Seattle television station. She had been a regent at the University of Washington since 1975. That year, she became the first woman director of First Interstate Bank and the first woman to serve as president of King County's United Way. She was later named to the national United Way committee and, in 1983, became the first woman to lead it. Her tenure on the national United Way committee is believed to have helped Microsoft at a crucial time in its development. In 1980, she discussed with then-IBM Corp. Chairman John Opel, who was also on the United Way committee, the business IBM was doing with Microsoft. Opel, some accounts say, knew little about the venture, but mentioned Mary Gates to IBM executives who introduced Microsoft at a meeting of IBM's top-level management committee a few weeks later. IBM contracted with Microsoft, then a small firm specializing in computer languages, to create an operating system for its first personal computer. Their success gave Microsoft a lift that eventually made it the world's largest personal computer software company. Sales now exceed $3 billion and her son is one of the nation's wealthiest men. In Seattle on Friday of cancer.