Texas Instruments Inc., the multibillion-dollar semiconductor and defense electronics company, yesterday announced that President and Chief Executive Officer J. Fred Bucy had resigned "in order to pursue other interests."

In a special board meeting, Texas Instruments directors named Executive Vice President Jerry Junkins, who oversees the company's government electronics, data systems and industrial controls businesses, to replace Bucy.

"We were surprised internally, too," said Norman Neuriter, a Texas Instruments spokesman. Bucy "basically said he's off to pursue other interests, and one should take that at face value. Jerry's accession here in no way indicates a precipitous change in either the strategy or direction of the company."

With roughly 43 percent of the company's $5.7 billion in 1984 revenue coming from semiconductor sales, Texas Instruments has seen its sales and profits slump along with the world market decline in computer chips.

The company's first-quarter earnings dropped from $3.32 a share in 1984 to barely 37 cents a share in the first quarter of 1985. Some analysts are predicting the company faces second-quarter losses.

"We are the world's largest manufacturer of semiconductors," said TI's Neuriter. "It is a very important business for us, but we're in a period where the world semiconductor market is in a definite recession right now."

"The semiconductor industry is in a rough situation, and in this market, TI's semiconductor division is hurting," said Frederick L. Zieber, a senior vice president at Dataquest. "My estimation is that the whole industry is down more than 30 percent from last year."

"It's going to be a break-even kind of year for TI," said Daniel L. Klesken, a partner with San Francisco's Montgomery Securities. "It'll be a tough year for them to make money. Revenues will be about $5.3 billion, and profitability will be somewhere between break-even and a dollar a share. But I don't think you'll see any major strategic change in the company."

Under Bucy and TI Chairman Mark Shepard, the company made a serious effort to diversify by trying to enter the consumer electronics market. An effort to sell digital watches failed in the early 1970s, and a major attempt to establish Texas Instruments as a home computer company led to a $660 million write-off in 1983. After the home computer fiasco, the company said it would focus on its semiconductor, defense and computer technology markets.

Bucy, 56, had been with Texas Instruments for 32 years. He has been active in public policy issues, particularly in education and technology export policy. A decade ago, he headed a blue-ribbon Cabinet-level commission that made several recommendations on how strategic export controls for high-technology products should be implemented.

Junkins, 47, has been with the company 26 years and is now regarded as Shepard's heir apparent. He joined the board of directors last year. According to both analysts and TI insiders, he gets along better with Shepard than Bucy did.

The company said Bucy will remain available to the company as a "senior adviser" to the board.