The full weight of the federal government is about to fall on Ronald Reagan.

Between now and election day, members of President Carter's Cabinet have been asked to reserve a total of 110 days for campaigning, according to John Rendon, the Carter campaign committee official in charge of coordinating the effort.

The Cabinet secretaries and dozens of their colleagues from the White House and other government agencies will fan out across the country, appealing for Carter's reelection before whatever constituent groups to which they have special ties. Many will bring with a timely announcement of some grant or other favor from the federal government.

The politics of incumbency, the inevitable phenomenon whenever a president is seeking reelection, is in full swing.

White House officials have never made any secret of their intention to use the full powers of incumbency in seeking to keep Carter in office. In 1976, they were on the receiving end of all that power, and they have not forgotten.

The White House has been putting those lessons to use for months, first in the Democratic primary fight against Sen. Edward M. Kennedy (D-Mass.), and now in the general election campaign against Republican nominee Reagan. They are a way for Carter, a president who has offended many of the traditional constituencies of the Democratic Party -- and many Democratic politicians around the country -- to make amends to at the politically most important time of his presidency. And Carter is doing so without even a hint of embarrassment.

The powers of incumbency are many and varied, involving favors great and small. But in a close election, such as this year's is expected to be, no edge enjoyed by the incumbent is to be overlooked. For example:

Michigan is a critical state to Carter, and is suffering severely from the downturn of the U.S. automobile industry. But Michigan has a friend in Washington. In the last several weeks, the friend has announced his willingness to provide $9.3 million for a gasohol plant, $1 million to retrain 1,000 unemployed workers, $29.8 million to Detroit and $1.6 million to Flint to provide summer jobs for young people, and $25 million to renovate a Detroit housing project.

Florida is another critical state to Carter, a bedrock of the president's southern base. But south Florida has been inundated with Cuban refugees, and its citizens were in open revolt against the administration. Last month, however, the White House moved to diffuse the anger by announcing the opening of a new refugee processing center in Puerto Rico to ease the burden on south Florida.

Brendan T. Byrne is a friend worth having, and keeping. He is the governor of a state Carter lost in 1976, New Jersey, and a longtime supporter of the president. Byrne teaches a course in government at Princeton University. This week the guest lecturer in his class is to be Jack H. Watson Jr., the White House chief of staff.

For three years, the president got along fine without a special assistant for ethnic affairs. Then, in February, with the 1980 election year in full swing, the White House hired Stephen Aiello, a former head of the New York City Board of Education. Aiello is paid $53,805 to look after the interests of mostly white, mostly Roman Catholic voters who tend to be clustered in the cities and suburbs of the major swing states. He joined a White House staff that already had similar special assistants for blacks, Hispanics, women, Jews and consumers.

Sept. 8 was a red-letter day for the city of Chicago. On that day alone, the administration was able to announce five grants for the city or its regional transportation authority totaling about $92 million. The next day Vice President Mondale visited the city. He was greeted at the airport by Mayor Jane Byrne, who had bitterly opposed Carter in the primaries, and she was all smiles.

On Labor Day, before an audience of labor leaders, Carter unveiled a new postage stamp honoring the late AFL-CIO president, George Meany. A few days before attending the dinner of the Polish-American Alliance, he personally announced the extension of $640 million in commodity credits to Poland for the purchase of grain. Last week he was in upstate New York to sign two documents of particular importance to the area legislation committing the federal government to pay for 90 percent of the estimated $225 million cost of cleaning up a former nuclear waste reprocessing plant, and an agreement with the state of New York, actually reached weeks earlier, to provide $15 million in grants and loans to relocate families living near the contaminated Love Canal.

There are, quite naturally, two different points of view when it comes to the politics of incumbency.

"They have been very bald about it up there, there is not even any pretense about it," said Paul Simmons, an aide to Republican Gov. James R. Thompson of Illinois, of the federal money that has flooded into Chicago.

"Traditionally, more than half our grants are released in the last quarter of the fiscal year," which ended Sept. 30, said Joe Marshall, an official of the Urban Mass Transit Administration, dispenser of much of the federal largess. "This happens every year."

But even when a grant is a part of the normal flow of federal business, there are ways for an incumbent to take advantage of it. The housing grant to Detroit is a good example.

Housing and Urban Development Secretary Moon Landrieu had a long-standing commitment to speak last month to the International Downtown Executives Association in Detroit. "It just so happened that we had a public housing grant ready to be announced for Detroit," said Gene Russell, HUD assistant secretary and Landrieu's chief spokesman.

Landrieu is among the high-level troops that Rendon of the Carter reelection committee is dispatching this month for the final push. The HUD secretary recently spent a full day spreading the Carter gospel in the Rio Grande Valley of Texas. A large turnout of the area's traditionally Democratic Hispanic vote is crucial to the president's chances of carrying Texas, which in turn may be crucial to his chances of winning reelection.

So Landrieu spent a full day going from town to town in the valley, meet-with local officials, hearing them out with a sympathetic ear. The trip had been suggested by Bob Beckel, the Carter campaign coordinator in Texas, as part of the effort to mend fences in a part of the state where Kennedy was strong in the primaries. Beckel said he suggested Landrieu because "he's known here [he is a former mayor of New Orleans], he's a warm guy, responsible, and a darn good campaigner."

Landrieu went to Texas bearing no gifts. But under the law, his department is required to announce at the beginning of each quarter of the fiscal year its urban development action grants. Some of the grants to be announced this month could go to one of the Texas town Landrieu visited. At the very least, the local officials in the area who are always looking for additional help from the federal government will have met personally with the keeper of the grant bag and possibly will have told their own constituents they have a friend in Washington.

Bob Beckel and Jimmy Carter certainly hope so.