The nation's largest thrift, Washington Mutual Inc., said Tuesday it is expanding further with a deal to buy rival H.F. Ahmanson & Co. for $9.9 billion in stock.

The purchase will create a company serving nearly 6 million households mainly in the West, including Utah, through more than 2,000 offices with nearly $150 billion in assets.The asset total would place it seventh among the nation's banking companies.

The deal by Seattle-based Washington Mutual comes only months after it outbid Ahmanson for Great Western Savings. Washington Mutual completed that $8 billion acquisition last July.

The combined Washington Mutual-Ahmanson will be called Washington Mutual Inc. and will be headed by Kerry Killinger, current president and CEO of Washington Mutual.

The merger is expected to result in consolidation of 3,000 to 3,500 jobs, or about 10 percent of the more than 31,000 people now employed by the two companies.

Washington Mutual also said it would consolidate 160 to 170 branches after the merger which is expected to be completed by October.

The deal should generate annual savings of $330 million by the year 2000, Washington Mutual said. It plans to charge $254 million against earnings for expenses related to the deal.