An hour after Dennis Donovan, a scientific illustrator at the National Bureau of Standards in Gaithersburg, learned he would be laid off, his wife Jane, a bureau secretary, was notified that she, too, would lose her job.

In one day, the Poolesville couple's combined income of $40,500, as well as their future, was placed in jeopardy.

"It hit me like a ton of bricks," Dennis Donovan, 33, recalled. "I was stunned."

Just a week before the April 13 lay-off notification, Donovan's superior had told him his job was secure.

After the news, Donovan said he felt his world had been turned upside down. He called 74 prospective employers seeking a new job. It was an arduous task but it paid off.

Three weeks after he became a victim of the largest reduction in force (RIF) in the agency's history, Donovan found a new post as a scientific illustrator with the Department of Defense. He'll begin work there June 1.

His wife hasn't been as lucky.

She ans many of the Bureau of Standards' 167 employes slated to lose their jobs by the end of September are still job-hunting or waiting for the bureau to offer them other positions.

Under the complicated RIF guidelines, each government agency laying off employes must attempt to place them in other jobs within that agency. Even if the new job is at a lower grade, the employe may continue to earn his or her previous salary for as long as two years.

Jack Vogt, a project director at the bureau who earns $49,002 a year, said he knew his job was threatened five weeks before his impending layoff was announced, but the knowledge only eased a painful blow. "It left me in a very uncertain position," he said.

"I see some people scurrying about, very aggressively looking for work in private industry," he said. "But I'm not rushing around looking for something else. I'm not in a hurry to find something I'll likely spend the next several years of my life in."

Vogt, 45, expects to receive an alternative job offer with the bureau, and he plans to accept it.

"My concern is that I'm not sure much thought went into this RIF," he said. "So many talented people are going to be lost to private industry. It's unfortunate the government has no system for keeping these talented people."

He added optimistically, "I'm a survivor, I'll make it."

Alexine Homes, 23, a $12,675-per-year physical-science technician in the bureau's dental laboratory, was the last hired, so she was first to go.

Since her work is highly specialized, she doesn't anticipate being offered another job at the bureau.

So she's busy with job interviews and is "thinking about leaving D.C."

"Best-offer" letters to employes being laid off from bureau jobs will be delivered beginning May 25, according to bureau spokesman Mat Heyman.

Such a letter either offers a new job within the bureau or states that no other job is available, Heyman said. The employe has 48 hours from the date of the letter to accept or decline any offer, and 30 days to move into any new slot. If an offer is rejected or none is made, the employe will be "separated" from the bureau within 30 days, according to a bureau paper on RIF procedures.

Heyman said the scheduled work-force cut is necessary to comply with personnel limits set by the Reagan administration.

The bureau already had 48 positions more than the 3,022 maximum set by former president Jimmy Carter.

A RIF of an additional 45 employes began last December and is continuing, Heyman said.

Dr. Ernest Ambler, bureau director, said in an April 13 memo all layoffs will be made during the current fiscal year "to minimize the instability which would occur if the RIF were delayed or done in several stages."

The bureau has hired two career counselors to help the affected employes. The counselors are paid $9,625 each for 50 day's work, Heyman said.

According to David Lesage, jobsearch assistance coordinator, the bureau maintains an up-to-date job-referral list and offers seminars on writing effective resumes and performance in job interviews.

Some 50 to 60 of the bureau's employes are taking advantage of the career counseling service, he said.