Dorothy Jenis, a high school teacher from Manchester, N.H., was invited to the White House last week. At the airport, she ran into E. Leo Kanteres, a Manchester real estate man, bound for a separate White House reception. At her hotel in Washington, she bumped into Maura Carroll, a friend from Concord, N.H. She, too, was on her way to the White House.

The three have one thing in common: each will be a Carter delegate to the Democratic National Convention. As such, they -- and scores of people like them -- are getting the full Carter massage.

With three weeks of primaries remaining, the Carter campaign is shifting into a convention and general election strategy. Maps of the convention floor have gone up at campaign headquarters. And an elaborate delegate tracking system has gone into operation, organized around where delegates will be seated.

Before Democrats meet to nominate a candidate next August, each Carter delegate will get the full "treatment." Each will be fawned over, consulted and cajoled.

Their names, ages, occupations, political history and concerns will be filed away in a computer. They will be telephoned and written to. And each will receive one -- maybe two -- invitations to the White House, according to Carter strategists.

"Our goal is to develop a close working relationship with each delegate by convention time," said Tom Donilon, Carter's delegate coordinator. "The Carter operation will be unrelenting."

The purpose is clear: the Carter campaign has gone into a full-court press to keep its delegates in line amid predictions from the camp of Sen. Edward M. Kennedy that many Carter delegates are "soft" and could be lured away.

The Kennedy camp is making a low-key effort to lure these delegates. It is focused on states where the delegate selection process is incomplete, according to campaign spokesmen. What contacts have been made with already selected delegates have come from Kennedy backers in the various states.

Part of the Carter effort is the same type of boiler room operation that every presidential campaign uses. But there appears to be unusual intensity and sophistication.

Each of the 1,474 Carter delegates elected to date has been sent a letter of congratulations signed "Jimmy," a second letter from campaign manager Tim Kraft, and has received a telephone call from the Carter camp. Woman delegates rate an extra goodie -- a digest of the Carter record from presidential special assistant Sarah Weddington.

There are no complete figures available on how many delegates have been wined and dined at the White House. But the number apparently is in the scores.

Dorothy Jenis and Leo Kanteres, both longtime Carter supporters, were invited for ceremonies around the opening of the new Department of Education. iAs a teacher, Jenis was a logical choice. But Kanteres, the New Hampshire Democratic finance chairman, has no direct interest in education.

"I was surprised to get the invitation," he said. "Of course, I've been to the White House before. I was there on St. Patrick's Day and last October when the Greek Orthodox archbishop visited."

Carter delegates are understandably impressed with invitations and attention. "I take special pride in the letter of congratulations I got from the president," said Irving Baskin, a delegate from Plantation, Fla. "I like to think the president wrote it himself. It's signed just Jimmy."

Baskin, 69, will be attending his first national convention. "I feel I'm not only a delegate, but I'm wanted," he added.

George Mendonca, political veteran from Kennedy's home state of Massachusetts, feels the same way. He was one of four Bay State delegates at a White House briefing on the economy two weeks ago.

"It bolstered my feelings towards the man," said Mendonca, a former state senator. "I was quite impressed with what the president predicted and I hope to God it comes true. He told us there'd be a turnaround in the economy in about four months."

Although plans for an elaborate delegate tracking system were laid last December, it didn't swing into full operation until recent days. It is organized around how the delegates will be seated at the convention.

Delegate coordinator Donilon has divided a map of the convention floor in his office into 14 "clusters." A desk officer is to be assigned to each cluster to oversee delegates in it.

If a telephone call from an administration bigwig, an invitation to the White House, or a handwritten note from the president, or some information about Carter's record would bolster a delegate's commitment, a desk officer is supposed to supply that.

The system should pick up any early signs warning of possible defections. Kennedy strategists contend that such defectors will come out of the closet if the Massachusetts senator scores several impressive victories in late primaries and if delegates become convinced that Carter would lose to GOP front-runner Ronald Reagan this fall.

Random telephone interviews with Carter delegates from New Hampshire, Connecticut, Illinois, Michigan, and Florida last week, however, found almost no support for this and very little softness in the support for the president.

"I don't see the kind of cracks that the senator is counting on," said Alfred Rioux, of Newington, Conn., in a statement echoed by many. "From what I've heard, I would be very, very surprised if there is a single delegate in Connecticut who would make a switch."

"I'd assume Massachusetts would be Kennedy's ace in the hole. If there were going to be any changes, they would come here," said one well-placed Boston delegate. "But I don't see any movement. That strategy is all wet."

A new party rule that each candidate must approve the names of delegates running in his behalf minimizes chances of "ringers" or political moles being selected to delegations. In some states, like Illinois, Carter delegates were selected last October when Carter was at rock bottom in the polls. Anyone agreeing to support the president at that time is likely to be a true believer, party officials point out.

"These delegates aren't strangers to us. They're not just people who walked off the streets," said Carter campaign chairman Robert S. Strauss."They are dedicated Carter supporters who have proven their loyalty."

The only area where interviews suggest softness in the Carter camp was in Michigan, outside Detroit.

Nancy Waters, a delegate from Muskegon, said she considers herself a "soft" delegate. "I've been a little disappointed in the president's leadership. Auto plants are closing all over Michigan," she said. "Every time I pick up the paper I read he's bungled something else. Boy, it's getting scary."