In the House, crossing Appropriations Committee Chairman Jamie L. Whitten is something like toying with Mother Nature. The veteran Mississippi Democrat, whose committee controls the flow of federal dollars to lawmakers' districts, can, if he chooses, call down all manner of political calamities upon those who displease him.

So when Rep. Buddy MacKay (D-Fla.) took the House floor shortly before midnight on April 23 to offer an amendment cutting $2.2 billion from the fiscal 1987 supplemental appropriations bill, he understood, as he put it, "that there were some career risks involved."

On its face, MacKay's amendment only asked Congress to live within the bounds of the fiscal 1987 budget it approved last year by cutting 21 percent from almost every program in the $11.3 billion supplemental spending bill. But more fundamentally, it represented a rare challenge to the authority of Whitten and the committee's "College of Cardinals" who are used to having their way, budget or no budget.

To the surprise of many, MacKay's amendment passed easily, 263 to 123, attracting support from across the political spectrum. Democratic Whip Tony Coelho (D-Calif.) called it "a significant vote" that demonstrated House Democrats are willing to force the Appropriations Committee to live within the budget and are eager to show the country that their party is not just for higher taxes but for fiscal discipline as well.

It was also a kind of political coming out for MacKay, a soft-spoken but determined lawmaker who is quietly becoming an influential player on budget issues in Congress. At a point in his career when many in Congress are still searching for a place to make their marks, the third-term 54-year-old from north-central Florida has become a leader of a group of relatively junior House Democrats who are having a noticeable impact on how the institution views spending issues.

Just how much of an impact may become clearer later this summer. MacKay and some of his allies from the Democratic Budget Study Group, joined by some Republican colleagues led by Rep. Rod D. Chandler (R-Wash.) are planning to use the next scheduled increase in the federal debt ceiling to force the Reagan administration and Congress to negotiate a long-term solution to the nation's budget deficit.

"As long as we're in a situation where one side is saying 'I'm willing to talk, but I won't discuss taxes,' and the other side is saying 'I'm willing to talk, but I won't discuss budget reform,' we can't resolve this problem," MacKay said. "You've got to say everything is on the table. I'm interested in a process that forces that bipartisan agreement. We typically don't do that until disaster is at our door and then we do it very quickly and very efficiently."

Because the almost annual battles to increase the debt ceiling afford legislators a chance to jam the gears of government, they are the perfect opportunity to increase leverage. The 1985 Gramm-Rudman-Hollings law mandating systematic reductions in the federal deficit was an amendment to the debt ceiling.

This year, the stakes are even higher because on July 17 the debt ceiling will be scaled back to $2.1 trillion if Congress does not vote to increase it beyond its current $2.32 trillion level. With the nation's outstanding debt already above $2.1 trillion, failing to raise the ceiling would mean the United States would default on its security obligations, with potentially devastating consequences in the marketplace. There is considerably more at risk than in the past, when delays in increasing the ceiling have meant only that federal employes had to be sent home from work for a couple of days.

MacKay, who worries about such things as the federal deficit and how much of it is bankrolled by foreign investors, sees July 17 as a dandy opportunity to focus attention on those issues.

"I am looking for some way to use the leverage of the debt ceiling to create a crisis," he said. "The fact that some people say that is irresponsible doesn't bother me in the slightest."

MacKay hardly fits the profile of a legislative bomb-thrower. A devout Presbyterian and an Air Force veteran, he was elected to the House in 1982 after 12 years in the Florida legislature, where capital reporters seven times named him the state's most effective legislator. Except for a liberal pocket around the University of Florida in Gainesville, his district is conservative Democratic, and MacKay, whose roots go back three generations there, is very much an establishment figure in his home town of Ocala.

Though MacKay seems low-key and moderate in Washington, he is no stranger to controversy and risk-taking at home.

As a state legislator, MacKay was known as a progressive Democrat who championed open government. In the state Senate, he was one of a half-dozen "Doghouse Democrats" who challenged the rule of the conservative kingpin of the legislature's upper chamber.

In Congress, MacKay has taken positions that rankle conservative voters in his district. Because he opposes aid to the Nicaraguan contras, not a popular stand in Florida, MacKay has been the target of a right-wing advertising campaign. "Right-to-life" groups have hounded him for being "pro-choice" on abortion and frequently picket his house and church.

Though MacKay's short-term political future seems relatively secure, his district is undergoing the kind of explosive growth that can spell trouble for an incumbent. Created four years ago, the district will likely be carved into two after the 1990 census because of rapid growth fueled by its popularity as a retirement area and an expanding thoroughbred horse-breeding industry.

Faced with that dynamic, other legislators might specialize in something with more glamor than the federal deficit, a subject that MacKay cheerfully concedes is "a ho-hummer, a root-canal issue."

Dull as it may be, MacKay spends a good deal of time in his district trying to educate constituents about what he sees as the dangers of high deficits and the perils faced by the country's new status as a debtor nation. On a visit home last month, for example, he met with a group of University of Florida economists to discuss the potential consequences of the national debt.

Though he came away from that meeting feeling that the crisis is not as dire as he thought, MacKay remains no less convinced that Congress is at a critical juncture in dealing with the deficit.

His solution is for everyone to share the pain: President Reagan must agree that higher taxes are necessary; Congress must consent to budget-process changes that ensure that its appropriations bills do not exceed the budget guidelines; all federal spending programs, including those like Social Security that are regarded as sacrosanct, must be subject to cuts, and a new automatic spending reduction mechanism must be restored to the Gramm-Rudman-Hollings balanced-budget law to impose fiscal discipline on Congress and the president.

"The whole thing is a mirror image of tax reform," MacKay said. "We couldn't solve tax reform until everyone agreed we were all in it, with no exemptions."

Though MacKay's views are far from universally held in the House, a solid corps of younger Democrats who are less wedded to their party's orthodoxies think along the same lines.

"Buddy and I say the same thing. We need more revenues and cut everything else," said Rep. James C. Slattery (D-Kan.). "If Democrats can't exercise restraint on the spending side, we have no credibility on revenues. Walter Mondale's mistake was you can't take tax-and-spend to the American people, but you can take tax-and-restraint."

MacKay's idea of using the debt limit to force Reagan to accept higher taxes and the Democratic-controlled Congress to accept budget-process changes may even become official Democratic strategy as congressional leaders try to implement their $1 trillion budget over the objections of the president.

Searching for ways to get Reagan to accept the $19.3 billion in new taxes contained in their budget, Democratic leaders may fold the debt limit increase and some version of budget revision into the tax-raising legislation that is scheduled for passage this month.

Ultimately, MacKay believes, that could provoke a confrontation between the White House and Congress that might lead to a true budget summit conference.

"That's all I want," MacKay said, "a situation where the risk of not doing something is as great as the risk of doing something."