LAFAYETTE, La. (AP) _ Oilfield service companies, buoyed by a mild rebound, are looking for workers and having a hard time finding them.

''We've hired 100 people in 90 days and I need 40 more people now,'' said Dailey Berard, president of Universal Fabricators.

''I see it as a serious problem for the industry to get back in the business,'' he said. ''The materials are not here, the personnel are not here and the expertise has been retired.''

Even so, the news is not necessarily as encouraging as it appears, one industry official says.

Chuck Barden, head of the Denver-based International Association of Geophysical Contractors, said he thinks the hiring may result in new wells - but not new sources of supply. That is because the drilling is in already known oilfields, he said.

Berard said 13 of 15 calls to former employees in Louisiana recently were answered by their wives with the news that their husbands are now working out of state.

''The wives have said they'd pass the word to them,'' Berard said. ''But they've migrated to other states and luring them back is going to be difficult because we can't pay the wages they're making now. So, it's a chicken and egg situation.''

Skilled laborers are a virtual necessity since the market is still highly competitive, but Berard said people with rusty skills should be able to get work after taking refresher courses in local vocational-technical or trade schools.

''We're advertising for structural welders and fitters in all the outlying communities and it looks like we'll have to go beyond that,'' he said.

At Schlumberger Well Service, district land manager Jim Malone said he was having trouble finding trained mechanical and electrical engineers.

''There's not a shortage of semi-skilled workers, but the engineers we hire have to be trained for at least six months,'' he said.

His office is three engineers short and has tried but failed to entice former engineers from other Schlumberger offices throughout the country into moving to Louisiana.

During last year's severe downturn, in which oil prices dropped to levels of $10 a barrel or less, Schlumberger engineers took advantage of a company offer to send them back to school to get master's degrees in exchange for a three-year commitment to the company.

Malone said a number of engineers have completed their studies and taken various other jobs.

He said oilfield activity is expected to increase in the next several months, and companies are adjusting their budgets for the anticipated upturn.

At Chevron, the experience was different. Ray Wilcox, Chevron's field operations superintendent, said he has had a limited number of new jobs and no trouble filling them. A recent ad for mechanics and electricians drew 200 applicants, he said.

In Tulsa, Okla., a spokesman for the American Association of Petroleum Geologists said the labor situation is tight in all the oil states.

''Oilfield workers by and large are semi-skilled workers, able to work in any given industry at any given time. Now, they've left this part of the country and gone to Atlanta, Kansas City, places where there's been work.'' said Larry Nation.

''They're not in the oil patch. And when the oil patch is finding itself with a need for people, they're not there,'' he said.

Although the labor shortages are real, Barden warns it does not necessarily mean the nation's energy problems are lessening.

In a telephone interview from Denver, Barden said that while drilling activity is up and petroleum equipment operators have been reporting increased business, seismic work for new exploration has not seen the same kind of improvement.

The number of working seismic crews stood at 160 in January and 187 in August, compared with a high of 744 in September 1981, he said.

''What this really means is that the U.S. oil industry is concentrating on production - drilling additional wells in known oil fields - and not looking for new ones, when we have to find new oil and gas,'' Barden said.

''People may think things are getting better now,'' he said. ''They're not.''