The cost of renting intellectual powers is going higher and higher. And the people bestowed with such powers are playing harder and harder to get. So, many companies are finding it more difficult -- and expensive -- to recruit and retain highly skilled employees.

It is customary for high-technology concerns, for example, to pay employees a reward for luring a skilled person to the company. But a chronic shortage of topnotch engineers, especially in hot high-tech areas like Boston's Route 128, has forced some companies to up the ante. Codex Corp., a maker of data communication equipment in Mansfield, Mass., offers a hefty reward to any employee who helps fill an opening. The bounty: $1,000 a head for salaried personnel, $500 for nonsalaried employees.

"It's a competitive and tight job market," says Codex spokesperson Judith Goldstein. "We need highly skilled people, often in extremely esoteric fields. It's particularly hard to get the best engineers in Massachusetts, because a lot of the high-tech companies here are growing quickly, and vying for the same talented people."

Goldstein says Codex promotes its recruitment efforts with posters, placed in office hallways and cafeterias, that proclaim different head-hunting slogans. One recent poster proclaimed a "Quest for the Best." In 1984, the company handed out more than $100,000 in bounty money.

Once they have found the right person, many managers have learned that they must keep him or her satisfied with sabbaticals. 3Com Corp., a $16-million manufacturer of personal computer networking equipment, even spreads the largesse beyond their tech-contingent. It encourages any employee who has been with the company for at least four years to take a sabbatical, with salary, during the fifth year.

The sabbaticals may not be novel, but 3Com has gilded the privilege by giving its 220 employees two uncommonly generous options: They can take six weeks at full pay, or they can take three weeks at double pay.

One theory behind the shorter sabbatical is that hourly wage employees don't earn enough to do anything spectacular for six weeks, but with double pay for three weeks they can. Another factor is that top executives are usually disinclined to step off the treadmill for long periods of time.

"This is a high-stress company in a high-stress industry," says personnel director Debra Engel. She points out that 3Com, located in Mountain View, Calif., has been growing at an annual rate of more than 350%. "The sabbaticals refresh and revitalize," explains Engel. "An employee can get away for a while and realize that his whole life isn't the company. But the sabbaticals are more than just burn-out prevention -- they're also a reward for four years of hard work."