President Michael D. Capellas, a key figure in the hard-fought battle over the HP-Compaq merger, will resign his position and is to try to resurrect fraud-plagued WorldCom.

During a five-month proxy battle for shareholder approval, Hewlett-Packard billed its billion takeover of Compaq Computer as a merger of equals.

Perhaps no one was more equal than Compaq CEO Michael Capellas, who was touted as the operations whiz necessary at the new company. He often shared the stage with H-P CEO Carly Fiorina and was a key spokesman for the merger. But six months after the merger closed, Capellas resigned Monday, apparently on his way to becoming WorldCom CEO.

The abrupt departure, while not unexpected, gnaws at some investors who thought Capellas would stick around at least a year. Some supported the controversial merger because of Capellas. The merger was ratified 51.4% to 48.6% in April.

''H-P knew Wall Street thought highly of Capellas, and smartly leveraged that appeal to gain a narrow victory,'' says David Katz, chief investment officer of Matrix Asset Advisors, which sold its 600,000-share stake in H-P this year. ''The fact he pushed it as hard as he did, while intending to leave this year, is mind-boggling.''

In December 2001, three months after H-P announced its intention to buy Compaq, Compaq's board rewrote Capellas' contract. Under the revised deal, Capellas would be paid .4 million if he left within a year of the merger's close in May 2002. The amended contract also specified Capellas wouldn't be CEO of the new H-P.

In the months since, Capellas has spent most of his time visiting Compaq customers and smoothing the transition to the new company. Only in the past month had he talked to WorldCom and two other companies about jobs, he said Monday. H-P shares rose 4% to .50 Tuesday.

H-P repeatedly used Capellas to help sell the merger. It positioned Capellas -- who is credited with shoring up Compaq after its rocky merger with Digital -- as an operations expert who complemented Fiorina's strength in marketing and strategy. ''In pursuit of the merger, (Fiorina and Capellas) did everything they needed to get it passed,'' says analyst Andrew Neff of Bear Stearns.

During the proxy fight, Capellas was coy about his long-term plans. When asked this year by executives at Institutional Shareholder Services, whose clients own 23% of H-P shares, Capellas said he ''enjoyed the operations side and looked forward to putting together the companies,'' ISS Vice President Patrick McGurn says.

ISS, which directly controls the vote for about 10% of H-P shares, supported the merger.

''No one had great expectations of him sticking around 60 months. But many expected more than six months,'' McGurn says.