The concept of putting the giant new MX intercontinental missile up in an airplane, an idea that has started one of the biggest battles over strategic weapons this capital has seen in 20 years, was developed by "two little guys from nowhere who were able to inject something into the process."

That's the way Ira F. Kuhn Jr., of B-K Dynamics Inc., a Rockville think tank, described the origins of their air-mobile MX, the so-called Big Bird that has caught the fancy not only of Defense Secretary Caspar W. Weinberger but apparently of President Reagan also.

On the other side, the top Air Force command is alarmed and defense establishment leaders on Capitol Hill are angry at the possibility that the Reagan administration will adopt Big Bird as a substitute for the expensive and controversial land-based MX system inherited from the Carter administration. The $50 billion land-based plan would hide 200 MX missiles in thousands of shelters in Utah and Nevada, while the air-mobile concept would put the new intercontinental missiles aboard fuel-efficient planes that could stay aloft for nearly seven days.

The "two little guys" Kuhn described in a telephone interview yesterday are himself and Abe C. Kerem, an Israeli aeronautical engineer who has been in this country for four years and runs Leading Systems Inc., of Los Angeles.

About seven months ago, Kuhn, a physicist, began working out a concept for an air-mobile MX which he said would "overcome the weaknesses of the past efforts, the vulnerability to surprise attack and endurance in the air." Among other things, Kuhn said yesterday, "half the fleet would always have to be in the air." He says he dubbed Big Bird after the character on TV's "Sesame Street."

Once Kuhn worked up the requirements, he turned them over to Kerem, whom he described as a "brilliant designer and engineer, a throwback to the 1940s when one man designed a whole airplane from scratch."

The plane that Kerem designed on paper employed "on-the-shelf technology," according to one defense expert who has reviewed the plan, in the form of composite materials for the large wings and tail that reduce the weight of the craft and four, fuel-efficient propeller engines that could use diesel fuel.

The Kerem airplane is designed to use one-fifth to one-tenth the fuel of air-mobile jets studied in the Carter administration.

With design in hand, Kuhn set about trying to sell it to the defense strategists inside and outside the Pentagon. After an initial turndown by one Pentagon research office, Kuhn decided in February he would approach the new commission established by Weinberger to study the MX, headed by Dr. Charles Townes, a Nobel prizewinning physicist from the University of California.

Using his friendship with one member of the commission and a staffer from its executive secretariat, Kuhn got an opportunity in March to brief several of the Townes commission personnel. That, in turn, led to a late-April presentation in Washington before the full panel. Using charts and viewgraphs, he talked for about 30 minutes about the plane's advantages, and then answered questions.

"I got a good hearing," Kuhn said. One friend on the commission assured him, he said, that "I got out unscathed, doing better than most of the others presenting ideas."

Within the commission, the members were intrigued with the Kuhn-Kerem design, primarily because "it was not particularly high technology," as one source put it, but also because the sharp reduction in fuel costs "became one of the few ideas worth looking at closely." Air-mobile concepts developed in past years were always rejected because continuous flying was too costly while keeping the planes on alert at airstrips made them just as vulnerable to Soviet attack as conventional bombers.

In May, the Townes panel asked both the Air Force and the Office of the Secretary of Defense (OSD) to take a look at the Big Bird proposal. Kuhn was not surprised when the Air Force showed no enthusiasm for his design.

The defense secretary's staff called on its Advanced Projects Research Agency to study the plan and, according to Kuhn, that turned out to be a "false start." They came out, he said, "doubting the plane would perform as well as we said it would though they found it technically feasible." In addition, Kuhn said, they did not look at its main advantages, its low cost and lack of vulnerability.

By early June, the Townes panel asked Boeing Co. to do an independent evaluation of the Big Bird plan. But before the major aircraft manufacturer was allowed to look over the proprietary data worked out by Kerem, Boeing employes were required to sign statements saying they would not disclose the material to other people in their own company -- thereby protecting the financial stake that the "two little guys" had in their new concept.

Kuhn spent two weeks in Seattle working with the Boeing group and in mid-June, he said, the company came back with "a very supportive finding." Boeing concluded that the plane, according to Kuhn, was "super good on cost and performance, and good on vulnerability."

Boeing's positive finding, he said, has been somewhat embarrassing to the company since some critics of the air-mobile concept are complaining that the aircraft manufacturer "had become an advocate" in hopes of getting the eventual contract to build the new Big Bird planes.

That criticism, Kuhn said, has "upset" Boeing in its relationships with the Air Force, partly because Boeing is also a major contractor for the land-based MX the Air Force hierachy favors.

Townes commission members have been publicly silent about Big Bird, but sources indicate that the high-endurance airplane Kuhn and Kerem propose is one of the ideas commission members find promising for the future.

In any case, the commission's study of Big Bird and the positive conclusions from Boeing drew the attention of Defense Secretary Weinberger, who has been eagerly searching for some solution to the MX question other than putting the missiles all across Nevada and Utah.

Review of the Big Bird concept paper was far from over after Boeing took its whack. The Townes group then directed that Kuhn sit down with the Air Force Ballistic Missile Office at Norton Air Force Base, Calif. Since the Air Force hierarchy was publicly, by this time, wedded to the land-based plan, Kuhn expected rough treatment at Norton. He was there for a week or two, he said, and it turned out as he expected.

"On their first cut," he recalled, "the Air Force found the plane would be a less expensive system than their own," the land-based approach.

"On their second cut, however," he remarked with some sarcasm, "they did things to it like increasing the crew and cutting down its time in the air...things all calculated to decrease performance and increase cost."

Kuhn professes not to know what the Air Force reported back to the Townes commission nor what Townes has told Weinberger, but it's no secret around Washington that Air Force officials are mounting a major counter-offensive against Big Bird, arguing that it won't work and will be more costly. There is some suggestion that leading Air Force generals may decline to support an air mobile program, even if Reagan proposes it, because they have spent years testifying against the concept on Capitol Hill. Kuhn's counter argument is that he and Kerem have come up with a genuinely new design, one which overcomes objections of the past.

Strangely enough, Kuhn said the defense secretary's office has never directly contacted him or Kerem since the proposal first entered the Pentagon's MX debate four months ago. Given what Kuhn now calls the "misinformation" being circulated by the Air Force about his air-mobile concept, he says it is "unfortunate he has not had a chance to talk to Weinberger."

Neither Kuhn nor Kerem has yet received any funds or government contracts for their efforts, Kuhn said yesterday, but he expects that, if the Townes group pays Boeing for its evaluation, he and Kerem will be paid for their role. Kerem also has proprietary rights to the plane itself.

One objection to the Big Bird approach is that, before the new plane can be designed and built, MXs would have to be placed on C5A jet transports as an interim measure. But Kuhn argues that, if a sole-source contractor is selected to build the new plane, the Big Bird aircraft could begin coming off an assembly line by 1986. If the contract is made competitive, he claims the first one could be completed by 1988. In either event, he argued, the entire fleet could be finished by 1990, the same date envisioned for completion of the land-based, multiple-shelter program for MX.

However the current debate turns out, Kuhn is still rather startled that a little think tank from Rockville and a one-man design team from Los Angeles could throw the entire Washington defense establishment into an uproar.

"I'm surprised I got as far as I did," Kuhn said. So is the Air Force.