Hoping to fill a vital niche in a growing market, Hewlett-Packard Co. and Genentech Inc. said yesterday that they have formed a joint venture to develop and market new, sophisticated electronic tools and instruments to automate gene-splicing operations.

"While the market for this kind of equipment is very small today, we believe that, over the next decade, it will be a billion-dollar market," said Lewis Platt, general manager of Hewlett-Packard's analytical products group.

The move clearly indicates that genetic engineering is on the road to automation, according to several analysts. Instrumentation is needed not only for research and development but for mass-producing the "biologicals" that result from that research. Hewlett-Packard's Platt likens it to the shift in automation in the automobile industry.

Hewlett Packard, an electronic instruments and computer company with 1982 sales of $4 billion, said that it will invest between $10 million and $20 million in the venture over the next five years. The new company will be called HP Genenchem. HP will own a majority interest in the firm.

According to a Genentech spokesperson, the company had been developing its own instrumentation and saw a joint venture with HP as the best way to bring its expertise to market. Hewlett-Packard co-founder David Packard sits on Genentech's board of directors.

In the past, researchers had spliced the various strands of DNA--the building blocks of genetic engineering--by hand. More recently, machines have been used to mix and weave the strands of DNA. However, machines that actually could recombine the lengths of DNA necessary to make interferon or insulin have yet to be created. "We're looking at the marriage of computers and analytical products in the process control area," said Platt.