President Reagan, who benefited from a wave of support among young voters in his reelection campaign, was asked at a political rally last October at the University of Alabama in Tuscaloosa whether he favored more federal aid to college students.

"There is government help now for one out of every two students in the United States," Reagan replied, "and we have no intention of reducing that."

Today, however, Reagan is seeking sharp cuts in college student aid -- a limit on the amount per student per year, and income ceilings for families to qualify. His budget office contended this week that there has been a spending "binge" on college loans and grants with a "shotgun approach that has indiscriminately sprayed assistance at students regardless of income for almost any conceivable type of education."

In this case and many others, Reagan has now shifted from a candidate who extolled many federal spending programs when running for reelection to a president asking Congress to cut or abolish the same programs.

Reagan did not break any of his big promises on taxes, Social Security, and defense spending in the budget he sent to Capitol Hill this week, but he has come a long way in a short time from the reassuring promises of his campaign that he could reduce the budget deficit without cutting other politically popular domestic programs.

He insisted in September that "we can make further budget cuts without affecting how much actually goes to help the needy." But by his own administration estimates, programs for the poor will be cut 5 percent next year. Critics such as the Center on Budget and Policy Priorities, an advocacy group for the poor, claimed this week that the Reagan cuts are even larger.

Reagan campaigned at the dedication of a Buffalo apartment complex built with federal housing aid for the elderly and handicapped, calling it "truly a great thing." This week, he proposed no funding for the next two years for the same federal housing program.

He acknowledged during the campaign that major revisions might be required in Medicare, the federal program of health care for the elderly, but suggested these would be "not in restricting the patient" but rather in controlling payments to hospitals and doctors. This week, in addition to proposing limits on payments to doctors and hospitals, he proposed that Medicare patients pay somewhat more for their care.

In October, in an interview with Scripps-Howard newspaper editors and reporters, the president said "we now have budgeted for going back to purchasing land for parks."

In his new budget, he said there will now be a "significant decrease in land acquisition," and the administration is proposing "a three-year moratorium on discretionary acquisition of recreation lands."

Reagan never mentioned possible cuts in veterans' benefits in a speech to the Veterans of Foreign Wars in August. Later in the campaign he said he would give veterans the "benefits to which they're entitled." This week, he proposed a means test that would limit free health care to veterans below certain income levels.

The president told the Farm Journal during the campaign that "without question" he would continue the existing dairy price-support program. This week, the administration proposed to overhaul the program.

He said at the Missouri State Fair last August that the Farmers Home Administration (FmHA) "will continue reaching out to help tens of thousands of farm borrowers hold onto their farms and stay in business." On a campaign swing through Iowa, he boasted that the FmHA had "doubled its regular operating loans for farmers" in his first term.

This week, he proposed major retrenchments in the FmHA program.

In his election-year budget message last year, Reagan said the administration was still committed to "filling the Strategic Petroleum Reserve." This year's budget proposes "an indefinite moratorium on further development and fill" of the reserve.

Beyond all these promises, the president avoided saying in his campaign how far he might go in trimming domestic programs in a second term. Instead, he borrowed a tactic from his 1980 campaign of claiming the budget could be trimmed by eliminating waste, fraud and abuse, and then cutting programs after the election was over.

He was asked in February of last year by The Wall Street Journal if he intended to cut veterans' benefits in a second term.

"I'm not going to discuss things like that and what we may do in a second term," he replied.

Office of Management and Budget Director David A. Stockman included in Senate testimony a year ago a list of possible cuts that formed the backbone of this week's budget. In an interview with Fortune magazine then, he mentioned possible cuts in farm programs, mass transit and college student loans, and added, "You could find several tens of billions to throw overboard."

But, he said then, "the point is that we have knocked on all those doors for three years and three budget rounds. And the result is that people want to have mass transit subsidies and middle-class subsidies for education. And the agricultural sector wants all those benefits.

"I can't see any time in this decade that we will have the kind of people in Congress who will abolish those things -- even if it is philosophically correct to do so."

This week, Stockman has been urging Congress to tackle all these politically sensitive programs. "We have no choice but to pare back in a fundamental and far-reaching way the built-in commitments, the built-in programs that are driving the budget" upward, he said.

The president, too, has changed his tune. The day after the election, he said he was "not going along with the idea that the only way you can cut spending is to eliminate or reduce some program." But in his budget message this week asking Congress to eliminate or reduce scores of programs, Reagan said, "The single most difficult word for a politician to utter is a simple, flat 'no.' "