Union, N.J. — The sea of silver hair turned attentively to Joan Mondale as she campaigned for her husband here at the Thomas A. Ehrhart Gardens last Thursday. Some senior citizens murmured their assent when Mrs. Mondale, wife of presidential candidate Walter F. Mondale, said aid programs such as school lunches, social security, medicare, and medicaid should not be cut.
A few nodded in agreement when she said the country needed a president whose foreign-policy solutions did not mean ''more guns, more bullets, more missiles.''
And afterward the senior citizens, almost all of whom said they plan to vote in tomorrow's primary, voiced their support for Mr. Mondale or for the Democratic Party.
Tomorrow's New Jersey primary is whirling toward a frenetic end. And voters - particularly specific groups targeted by the three campaign staffs - are being pursued steadily.
''One thing we learned in Indiana was that people make up their minds late,'' says Marc Dann, field coordinator for Gary Hart in Essex County. His crews have ''backloaded energy'' for the final 78 hours.
Indeed, some political observers say New Jersey voters may well be saturated after earlier heavy campaigning in neighboring New York and Pennsylvania. People are hardly listening to issues anymore, says Albert Burnstein, a former state assemblyman.
They've been ''talked to death'' and find that the candidates' stands are not dissimilar, he says. Many voters will make their selection based on a candidate's personality, he adds.
Campaign strategies, whether intended to or not, emphasize image. Mrs. Mondale was busy visiting stalwart supporters of her husband - senior citizens, factory workers, and people at day-care centers. At Ehrhart Gardens, she spoke of family values and talked proudly of her three children.
Gary Hart supporters say they are trying reach traditional Democrats. But the blue-jeaned volunteers, handing out pamphlets to commuters going to and from New York, probably get the best response from the young, white-collar groups that have been strong supporters of Hart in the past.
And in keeping with their efforts to reach the ''locked out'' voter, the Rev. Jesse Jackson's supporters describe their operation as a ''poor people's'' campaign. Their workers do not hold media events with the press trailing behind because this campaign is being run at a grass-roots level, says one volunteer.
What do New Jersey voters think about the election?
Many are intent on ousting Reagan, but not all agree. An older man, a Democrat, who was shopping at a mall in North Edison, says he doesn't like all the cuts made in the last 31/2 years, but he thinks the economy is looking better. ''I think you have to give Reagan credit for that.''