Back in January, when the presidential political battlefield was Iowa and one of the leading issues was the embargo of grain shipments to the Soviet Union, Sen. Edward M. Kennedy (D-Mass.) saw an opportunity and quickly seized it.

Kennedy promised that, as president, he would never embargo grain except in time of war. And to the skeptics among Iowa's farmers, Kennedy said that a check of his 17-year record in the Senate would show that he kept his commitments.

At the Washington headquarters of President Carter's reelection committee, Kennedy's statement jogged the memory of Martin Franks, who knew something about the senator's record.

"I had a real hunch that since the previous embargoes were under Nixon and Ford, there was a good chance that a liberal Democratic senator would have said something about them," Franks recalled recently.

Files were checked, and the statement was found. Carter-Mondale headquarters hastily prepared a press release, and three days after Kennedy made his embargo promise a story appeared on the front page of the Des Moines Register with this lead:

"Carter-Mondale campaign officials in Washington passed out documents Friday showing that Sen. Edward M. Kennedy advocated restricting grain exports as a diplomatic tool in 1973."

"He just walked right into it," Franks said with a grin.

The Iowa caucuses, which Carter won easily, didn't turn on the issue of the grain embargo, but Franks demonstrated how quickly he could pin back the president's opponent on a small slip of the tongue.

Today Franks, a 29-year-old political science graduate of Princeton University, has begun turning his attention to Ronald Reagan.

Franks and his staff of two volunteers have been collecting material on the former California governor for the last several weeks, much as last fall Franks dispatched a group of volunteers with pocketfuls of chance to the Xerox machines at the George Washington University library to begin making copies of Kennedy's Senate voting record.

It is a far difficult task to research the record of a governor who has been out of public office for five years than a sitting U.S. senator. But judging by the early outlines of the Carter strategy for a general election campaign against Reagan, Franks' research operation may be more important to the president in the fall than it has been through the winter and spring primaries.

From Carter campaign chairman Robert S. Strauss on down, the president's political operatives say their best chance of success in the fall will be to make Reagan the issue, to get the public to question whether the former governor is, in Strauss' words, "a man of presidential caliber."

Central to this strategy will be Reagan's past and present positions on national issues, and his ability to deal with the complexities of those issues. And while the Carter-Kennedy race has produced few instances such as the embargo dispute in Iowa, there already has been a spate of stories questioning Reagan's grasp of some of the facts he throws out during campaign appearances, which the Carter aides hope is just a preview of what the fall will bring.

For the moment, Franks is concentrating on Reagan's more recent record, beginning with his 1976 GOP primary campaign against then President Ford. The Carter campaign also is culling Reagan's statements at his countless Republican fundraisers, and eventually will tap friendly sources in California for information on Reagan's record as governor.

Out of this, Franks said, should come information to keep public attention focused on Reagan's major proposals and positions.

"The larger task will be to show people that there is a difference between running around saying things everyone agrees with -- like 'let's make America great again' -- and picking apart what he says and pointing out that this guy has just not thought things through," he said.

The Carter campaign is looking forward to debates with Reagan in the fall, when the facts and figures being assembled by Franks will be used to prepare the president. In 1976, Carter, himself then a former governor with no Washington experience, discovered in his first debate with Ford that an incumbent president is a formidable debating foe.

Perhaps suggesting one reason that the president refuses to debate Kennedy but is eager to take on Reagan, Franks said:

"Anyone running for president, especially a non-Washington figure, has such a tremendous amount of information to assimilate in a short period of time that anyone would have a hard time doing it. A senator pick's up a lot of this by osmosis. But he [Reagan] has a whole lot of information he has to cram into his head in the next couple of months and it's a difficult job to do."