HONEYWELL TO BUY SPERRY AEROSPACE

Honeywell Inc., the Minneapolis-based computer and controls company, said today that it had agreed to purchase the Sperry aerospace group of the Unisys Corporation for $1.03 billion in cash.

The acquisition is expected to make Honeywell a much more potent competitor in the commercial and military aerospace industry. Sperry's aerospace unit, best known for its flight controls and instrumentation systems, is an ideal complement to Honeywell's gyroscopes and guidance and navigational equipment, analysts say.

The announcement capped months of negotiations between the two companies. The sale price, more than $300 million higher than Honeywell had originally offered, indicates how important Sperry's defense business is to Honeywell's future.

Complementary Operations

''They needed this business real bad,'' said Steve Binder, an analyst with Bear Stearns & Company. ''Now they can round out their product line and complement their other businesses.''

Honeywell had said in September that it was negotiating with NEC Corporation of Japan and Groupe Bull S.A. of France to take over a large stake of its languishing computer business. Honeywell has not said what might come out of those negotiations, but industry officials say the company is expected to surrender a large part of its information systems - which accounted for nearly a third of its $6.6 billion in 1985 revenues.

If its information systems were to be significantly reduced in size, military contracting would become Honeywell's biggest business. In 1985, Sperry's aerospace operations earned about $74 million on $700 million in revenues. Honeywell's defense unit reported operating income of $124 million, on revenues of $1.89 billion.'Cockpit of the Future'

''This is one of the most important acquisitions Honeywell has ever made,'' said Edson W. Spencer, Honeywell's chairman and chief executive. He said the combination would make Honeywell an important supplier for the ''cockpit of the future.''

Company officials said they did not expect the Federal Government to challenge the Sperry acquisition, in light of Honeywell's proposed deal with the two foreign computer companies. Typically, the Government takes a dim view of liaisons between its important military contractors and foreign companies.

Jay P. Stevens, an analyst with Dean Witter Reynolds Inc., said it was likely that once the negotiations with NEC and Groupe Bull were completed, Honeywell would receive a one-time payment that would be used to help finance the Sperry purchase. ''They're independent deals, but they're tied together,'' Mr. Stevens said.

Unisys, the new name taken by the combined Burroughs and Sperry corporations, said the proceeds from the sale would be used to reduce the debt associated with Burroughs's $4.8 billion acquisition of Sperry. Burroughs, which is based in Detroit, said it expected the deal to be completed by the end of this year. Last week, Burroughs agreed to sell part of its Memorex disk-drive business for $550 million to a group of company executives. Unisys said the sale of Sperry's marine and microwave group was ''currently being discussed with interested parties.''

A Unisys spokesman said the company planned to retain its defense systems unit, based in McLean, Va. That division makes radar and submarine navigation systems.Joining Top Military Suppliers

Honeywell's leap into aerospace defense will rank it among such leaders as the Rockwell International Corporation, the Bendix divisions of Allied-Signal Inc., and the Lockheed Corporation. But Honeywell is increasing its stake in defense just as the market for military suppliers is beginning to shrink.

''We're looking at a difficult budget environment where there will be more competition within the industry to win what business is out there,'' said Jerry Cantwell, an analyst with First Manhattan Company. Military procurement, which nearly tripled, to $96.8 billion in the fiscal year 1985, from $35.1 billion in 1980, is expected to fall to $92.6 billion in the fiscal year 1986, according to the Department of Defense.

''Honeywell paid $1 billion for a company at the top of the cycle,'' said Gary Reich, an analyst with Wertheim & Company. ''Everybody selling knows that. But in the long term, it is really a good acquisition.''

Honeywell closed at $71 today on the New York Stock Exchange, up 37.5 cents from Thursday.