The Marines will land in Turkey next month in hopes of demonstrating that they could anchor either the northern or southern flank of NATO in a war.

The exercise dramatizes the new emphasis U.S. military services are putting on Europe now that Vietnam is a war to forget.

This shift from the Pacific to the Atlantic is most pronounced for the Marine Corps - a service that has not fought in Europe in a major way since World War I.

Marine leaders, while acknowledging they have never concentrated so hard on Europe as they are today, stress tht they are not abandoning the Pacific. Instead, they said in interviews, the corps is pointing itself at the biggest threat to national security - a thrust by Warsaw Pact frces.

Crities of the corps, among them the Brookings Institution and Rep. Les Aspin (D-Wis.), contend the Marines are a servie in search of a mission now that the glory days of amphibious landings are over. "They're in trouble," said Aspin.

Gen. Alexander M. Haig, NATO commander, is looking past the roles-and-mission argument and urging the Marines to land in force to reassure European alies. THe name of the September exercise in Turkey is "Display Determination."

Last year about 8,000 Marines landed in Norway on NATO's northern flank. This time about 6,000 backed by Marine warplanes, will land in Turkey to show the versatility and punch of the corps on the southern flank.

NATO war plans long have called for the corps to serve as the "strategic reserve" - meaning Marines could be called in to plug holes in Army lines. But Marine leaders hope to show that the corps' versatility and speed deserve a different role.

"We can be best used on the flanks," said Marine Commandant Louis H. Wilson, adding that of course the corps wilt of course the corps will go wherever it is sent. He rejected the argument that the corps does not have enough armor and firepower to stand up to the Soviets.

"I would resist mightily being organized into tank divisions," said Wilson in arguing that the corps is heavy enough to clobber any enemy be exploiting speed and maneuveablity. "We have no desire to be a second land army. We have the capability of doing whatever is necessary, and indeed we are ready." The corps has never been as ready as it is today, he said.

Lt. Gen. Robert H. Barrow, commander of the Fleet Marine Force in Norfolk, which will send the airground team to Turkey, shot at the "not heavy enough" argument from another angle.

"We have at least reached the threshold and maybe crossed it in making the tank obsolets, or near obsolete, on the battlefield," he said.

Conceding "those are strong words." Barrow continued: "We're reaching the point where some guy tucked away in the woods over there with a precision-guided weapon is going to knock the bejesus out of that 60-ton tank, which hasn't seen him because he's all buttoned up. Ten years from now the guy who brings a lot of tanks to the battlefield may be bringing liablities rather than assests.

"When you ask most people why we have the tank, they give you a very bad answer: 'To fight other tanks.' I'd like to have better odds than that," continued Barrow in arguing that putting one modern tank against another would be like betting your life on one of two evenly matched boxers.

The more sensible roles for tanks in this era of the smart weapon, Barrow contended, are for "shock action, mobility and firepower."

What technology has done for the infantryman "boggles the mind," he said. The corps, he added, is exploiting that technology and would not be tool light for any armor the Warsaw Pact sent against it.

Whether U.S. military forces should be restructured in Europe and elsewhere to take maximum advantage of smart weapons is one of the many questions White House, Pentagon and State Department specialists are pondering.

The first decisions stemming from this exercise are expected to be sent to Congress in January.

Asked if in the meantime Carter is folloing the national military strategy he inherited form the Nixon-Ford administrations, Gen. George S. Brown, chairman of the Joint Chiefs of Staff, responded: "Defense guidance has not been revised."

The "defense guidance" when Robert S. McNamara was Defense Secretary from 1961 to 1968 was advertised as enough troops and weapons to fight one bigh war in the Pacific, anther in the Atlantic and a small war somewhere else - the 2 1/2-war strategy.

The Vietnam war showed with embarrassing clarity that the 2 1/2-war strategy was overambitious. Defense Secretary Melvin R. Laird, who took over at the Pentagon in 1969, embraced a 1 1/2-war strategy - enough forces for one bigh war and one small one. The 1 1/2-war policy is still the rough guidance, with the "one" clearly identified as Europe rather than Asia since the end of the Vietnam war in 1975.

Both civilian and military leaders sense that the American people have no stomach for fighting anothe Vietnam; that national interests must be clearly threatened before there is any next time.

Lt. Gen. Lawrence F. Snowden, Marine chief of staff, is among the military leaders who have sensed this change and are helping to shape the corps to conform to it.

"I just don't believe the United States is going to go to war again over a political ideology," he said in an interview in Marie headquarters.

"We're just not going to rescue Country X from some blackhat guys who want to take over the government."

Vietnam "fortified" the gut feeling of the American people that "just a war in the name of politics, that is, the ideology of the government, is not a very good basis for committing our people and resources a long ways from home."