MINNEAPOLIS, JULY 12 -- Citing differences in management style with chief executive John Rollwagen, Cray Research Inc. officials said today that Marcelo Gumucio, president and chief operating officer, has resigned effective immediately.

In a letter sent to employees today, Rollwagen said he and Gumucio ''were unable to agree'' on the execution of a long-range strategy for the supercomputer company.

Gumucio becomes the third key employee to leave Cray in the last few years. Steve Chen, a computer designer who many thought was the heir to Seymour Cray, left in 1987, and Cray himself left last year.

''We attempted to blend our distinct management styles effectively, but were not successful in that effort,'' Rollwagen said in his letter. ''The decision to part is mutual and in the best overall interests of the organization and the individuals involved.''

As the supercomputer company has grown to $780 million in annual revenues, Gumucio has tried to institute a more formal, structured approach to management, analysts say. That included detailed forecasting and goal-setting in an attempt to create more certainty in the business, Rollwagen said. Rollwagen served as its visionary, said securities analyst Gary Smaby of the Smaby Group.

''It hasn't been a problem for the two of us, but the rest of the organization is having trouble with our differences,'' Rollwagen said. ''There have been some mixed signals and confusion. While it hasn't caused any damage, we agree it's not good.''

Rollwagen wants to retain the company's informal, entrepreneurial approach.

''I am more inclined to set high targets and go for it, and work it out as we go along,'' Rollwagen said. ''I accept a high level of uncertainty and risk.''

After ''a long talk'' earlier in the week, Rollwagen and Gumucio agreed that it would be best for the company if one of them resigned.

''This is unexpected; however, over time it was clear that there was a difference in approach to management style,'' said Barry Willman, a securities analyst who follows Cray for Sanford C. Bernstein & Co. in New York.

Willman did not expect the resignation to have a substantial impact on the company, and said he maintains his positive outlook on the company's future.