Laverne and Charles Grady invited their congressman, Andy Maguire, to their Christmas eggnog and buffet party and he came. It was one of several quick stops Maguire made in a day driving the roads of northern New Jersey during a snowstorm.

Richard Leone is having two additional telephone lines installed in his Princeton home.

When floods hit Lodi, N.J. former New York Knick star Bill Bradley arrived to offer sympathy.

Jeffrey Bell, a fourth man in his 30s, but unlike the other three a Republican, is also traveling the state and making lots of extra telephone calls.

All of them have succumbed to a desire to be in the U.S. Senate and all have been reading polls and tea leaves that tell them the incumbent, Republican Sen. Clifford Case, is vulnerable.

New Jersey Senate campaigns are usually not as lively and hotly contested as this one promises to be. Case has been in the Senate since 1954 and Sen, Harrison A. Williams, a Democrat, has held his office since 1958. Obviously, a politician could get frustrated waiting for a glance at the Senate in New Jersey.

Why do so many see an opportunity to beat Case in 1978? "I think it's because of his age," an assistant to the 73-year-old senator said. "They say age should not be an issue and then keep on talking about how they don't want to make it an issue."

Maguire doesn't talk about age directly, but says Case has "a classic profile of an incumbent who has been in office too long." The liberal Democrat who is basing his compaign (with obvious reference to Bradley) on his record in Congress, tells potential contributors and supporters that he represents a no-lose proposition for liberals - they can switch from liberal Case to liberal Maguire.

While airing his attack at Case, Maguire keeps his guard up against Bradley.

"He's a good basketball player," Marguire told one group of potential contributors who left their homes in the snowstorm to listen to him, "but when you're in Congress you've got to hit better than 60 per cent from the floor."

Bradley is in the odd position of being both the frontrunner and the unknown quantity.

He is in the process of developing issues and thinking about campaign strategy, but knows that he will stress urban needs, jobs, health care and better use of government resources. After he formally announces his campaign next month, Bradley said, he will spend 18 hours a day campaigning.

Although his rivals cannot judge yet how effective a campaigner Bradley will be, they are worried about being able to raise enough money to match him.

Bradley is the only Democrat with personal wealth and the campaign finance laws permit unlimited spending in one's own campaign while other contributors can give a maximum of $1,000.

"Bradley calls the tune on money," says former State Treasurer Leone, the third Democrat who has opened a campaign office. "How much does he want to spend?"

Bradley said his campaign for the June primary will cost about $750.000.

Leone, who has been active in New Jersey politics for 15 years while teaching at Princeton, managed Gov. Brendan Byrne's upset re-eletion campaign this year and although he is less well known than Bradley or Maguire, he has won an early skirmish.

All three consulted David Garth, the New York media man who is riding an extraordinary winning streak after handling the come-from-behind campaigns of Byrne New York Mayor-elect Ed Koch and Carol Bellamy, who will become New York's next City Council president.

Garth chose to do Leone's campaign, picking another long-shot.

Leone, Maguire and Bradley have a common campaign theme in their criticism of Case for being a senator more concerned with matters of national and international policy than with policies that directly effect New Jersey.

Leone says, "I'm not trying to escape to Washington," and calls Case "an extreme example of non-involvement" in local and state issues.

Bradley, who has coined the phrase "citizen-politician" for himself lest anyone invent another phrase to describe his lack of political experience, says: "Case hasn't personally been involved in the state of New Jersey."

"He doesn't feel he neglects New Jersey," said Case's administrative assistant, Frances Henderson. "He really likes being a senator," she added. "Other than the governor he's the best-known politician in the state."

According to polls taken by the Eagleton Institute of Politics at Rutgers University, that is true. But the vulnerability is rivals see is that Case was identified by only 19 per cent asked the month before the election to name the Republican candidate.

An official of the institute said name recognition of politicians other than the governor was always low in New Jersey.

Like the Democratic candidates, Bell, who will take on Case in the Republican primary, has been looking at polls that Case's popularity is declining - the opposite of what usually happens to long-time incumbents.

Bell is a former adviser to Ronald Reagan and hopes to capitalize on the perceived rightward realignment of Americans.

Case is relying on New Jersey Republicans' memories of 1964 when the party lost office after office with Sen. Barry Goldwater heading the ticket. Although former President Ford carried New Jersey last fall, Case believes the state party doesn't want a Reagan Republican as its candidate.