The Agricultural and Mechanical University of Texas is known for its cadets, whose stiff marching boots and khaki uniforms make the campus seem frozen in the war years; for its football coach, Jackie Sherrill, whose $267,000 salary exceeds that of most university presidents; for its former economics professor, Phil Gramm, the irascible congressional budgeteer; for its petroleum engineering school, best and largest in the nation, and unavoidably, for its nickname, the Aggies, and the 101 dumb jokes inspired by that hayseed symbol.

The cadet corps has regained prestige in the "America's Back" era. Sherrill is threatening to earn his keep with an 8-and-2 team that is Cotton Bowl-bound if it defeats the University of Texas in Austin today, the first time since 1943 that the grudge match will decide the Southwest Conference title. Gramm is on one of his rolls in Washington, D.C., with another budget resolution named for him. And the 10th generation of 101 Aggie jokes has hit the streets with such entries as: Two Aggies went bear-hunting. They saw a highway sign that read "Bear Left," so they went home.

But there are hard times at the petroleum engineering school.

For two decades A&M's oil students, known as "Pet Es," were part of an extraordinary success story. From 1962 to 1982, every student in the department had a job in the energy industry before the diplomas were handed out.

Even those near the bottom of the graduating class had multiple job offers. The plant visits they took to oil company offices in Houston, New Orleans, Denver, Dallas and Los Angeles were much like the on-campus trips of blue-chip football recruits. They drew starting salaries of $32,000, about $3,500 more than mechanical and civil engineers were drawing.

The money is still there, but many of the jobs are gone, diminishing each year since 1982 when the industry went bust. And as the jobs have disappeared, so have the Pet Es. There are few more precise ways to measure the health of oil and gas than by examining the enrollment at Texas A&M's petroleum engineering school. "We are a barometer of the outside world," said Dr. W. Douglas Von Gonten, head of the department. "We are directly tied to the industry's supply and demand."

In 1981, when oil sold for $35 a barrel, 1,717 Aggies were enrolled in petroleum engineering, making it the largest major on campus. Freshmen were signing up at a rate of 600 a year. Classes were split into six sections of 45 students, with courses held evenings and weekends at the W.T. Doherty Petroleum Engineering Building, named for Doc Doherty, a former Pet E who made millions in the business. The faculty of 28 professors and associates took on double the workload recommended by the state. They could not get graduate assistants to share the teaching burden because virtually all the seniors were leaving for oil companies every June; only 35 stayed for graduate school.

Four years later, oil sells for $25 a barrel, and the Texas A&M undergraduate department is about one-third its previous size. There are 682 students, and the numbers are expected to drop even further: This June, 220 Pet Es will graduate and only 100 freshmen are expected to take their places. The graduate school, meanwhile, has grown to 100 students, in part because jobs are no longer waiting for them. After a 100 percent record for 20 years, job placement for Pet Es dropped to 50 percent in 1982 and 42 percent for 1983 and 1984. Von Gonten is optimistic that it will return to 50 percent this year, reflecting not an industry recovery but smaller class size.

Similar troubles have hit petroleum engineering schools everywhere. At the University of Texas in Austin, enrollment has dropped from 1,119 students in 1982 to 333 this fall. The precipitous decline at UT comes just as the department is opening a large new building with high-tech laboratories, a facility planned during the boom years.

Texas A&M has had an oil engineering school since 1929, and for much of that time it has been the biggest and the best. In an average year, it graduates 15 percent of the new petroleum engineers in the country. The most recent edition of Gourman's quality rankings of undergraduate programs listed A&M first, followed by Stanford, the Colorado School of Mines, Oklahoma, Louisiana State, Texas, Tulsa and Kansas. Graduate programs at Wyoming, Penn State, California and Southern Cal also were highly rated. But when large oil companies need drilling, production and reservoir engineers, they often turn first to the Aggies.

This is the recruiting season, and in recent days personnel officers from Arco and Exxon have visited the campus. Amoco used to be the top recruiter at A&M. Now it is Arco, which has profited from production along Alaska's North Slope. "They've had the best cash flow, which means they've had to invest the money in operations, which means more people," Von Gonten said. "They've been our best source in recent years, followed by Mobil, Sohio, which is also on the North Slope, Exxon and Chevron."

The school is so closely tied to these companies that it suffers not only when oil prices drop but also when there are mergers within the industry. It seems that each time two companies merge, A&M loses research support and scholarship grants. Gulf and Chevron were big supporters of the school, but when they merged they donated half of what they had been giving as separate institutions. The same thing happened when Mobil swallowed up Superior, and when Texaco merged with Getty.

"Whatever happens in oil and gas, we feel it here," Von Gonten said. "But I feel pretty good about the way things are going. I feel sorry for students who graduated in the last four years, but there was nothing we could do about it. Supply and demand is something you just can't predict. All we need is another crisis, war in the Middle East, or any type of crisis where the flow of oil is threated or interrupted. Then our Pet Es will have plenty of jobs again."