The students are back! The students are back!

Each weekend they pour into New Hampshire by the busload -- dozens of student volunteers who spread the campaign word for presidential candidates by knocking on doors, passing out leaflets, and manning telephone banks.

Although most college campuses sat out Jimmy Carter's drive to the White House four years ago, many students today show no signs of letting presidential politics pass them by in 1980, political observers say.

Most organizers agree the number of students out pounding the pavement does not now compare to the tremendous surge of campus supporters who rallied around Sen. George McGovern in 1972. But campus volunteers have nonetheless become what one campaign spokesman calls "an incredibly valuable commodity."

Spurred at least in part by issues such as nuclear power and draft registration -- but fed also by a broader desire to "really change the course of American politics," as one University of New Hampshire senior puts it -- growing numbers of students are volunteering their time and energies for candidates of both political parties.

They have been converging on New Hampshire every weekend since early January. This weekend, with less than two weeks to go before the Feb. 26 primary, scores of students from all over New Engaldn and the East Coast will flood the state:

* An estimated 174 students from Yale, Brown, and Princeton universities, and from campuses in the Philadelphia area, will be bused in to canvass for Republican front-runner George Bush.

* Organizers for Sen. Edward M. Kennedy -- who recruited at least 875 New England students to blitz Maine for the Feb. 17 caucuses there -- say they plan to send at least 300 students now, and as many as 500 to 1,000 the weekend before the primary.

* Another 20 to 30 students will drive from Massachusetts to campaign for California Gov. Edmund G. Brown Jt., and several dozen are expected to turn out for Rep. John B. Anderson's GOP presidential effort.

* At the White House, 200 campus leaders -- including student body presidents and student newspaper editors from across the country -- have been called for a day-long "briefing" Feb. 15 on energy, foreign policy, and domestic issues. The students, who were notified of the meeting by Mailgram just seven days ago, will meet with top administration officials and possibly Mr. Carter himself, according to the White House.

In addition to their community canvassing, students spearhead voter registration drives on campuses, where they also set up information tables on a daily basis. But they are particularly prized by candidates because, unlike other campaign workers, their time generally is not tied down with jobs or to family commitments.

"Other volunteers just can't work on things all day and all night the way students can," says Anderson political director Kirk Walder, who estimates that 80 to 90 percent of the congressman's New Hampshire army is made up of students.

With the Federal Election Commission ruling that holds each candidate to a spending limit of $16 million, campaign organizers find that the more student support they can enlist, the more money is left to target for other costly items , such as television commercials.

"Students were a tremendous advantage for us in Maine," says Rick Stearns, who works out of the Kennedy national headquarters in Washington. "They offered us muscle which compensated for the money we didn't have.

"For us, the impact in the long run is enormous," he continues. "In Iowa, we had to pay for everything -- people to man the phones, do the staff work. The student support we've been getting relieves that financial pressure.We can count on this reservoir of volunteer help."

Most observers agree that, in the wake of the Iowa caucus, the prospect of the draft raised by President Carter in his proposal to register young men and women sparked a growing student support for Senator Kennedy. Governor Brown also has won favor among students for his unequivocal opposition both to the draft and to nuclear power.

"But it's not just the draft . . .. The problem today is that the whole system isn't running well," says Maureen Kennary, a Boston College student who plans to spend a week of school vacation campaigning in New Hampshire for Mr. Anderson.

Although the heaviest student involvement so far is focused on the coming primaries in New Hampshire and Massachusetts (on March 4), student organizing already has spread across the country.

According to Karen Jones, national youth organizer for the Bush campaign, statewide student Bush groups are under way in 30 to 35 states. Kennedy coordinators say students in California, Texas, Ohio, and Michigan already have begun their own organizations -- even without prompting from the Kennedy staff.

"I haven't had this kind of success recruiting on college campuses in years," says Greg Akili, a student organizer for the Brown campaign. "There's a revitalization among young people to get involved again . . .. They're not coming for a lark. They're coming because they're serious about getting involved."