The nation's home builders, a little to their own surprise, are bucking the White House and lobbying hard to defeat the Republican budget plan in the House this week. They fear it would rule out housing bailout bills of the sort now pending in both houses.

Eastern Airlines has emissaries at work in the House this week, too, but it is supporting the Republicans.

Their plan calls for the smallest tax increase of any of the three major budget proposals in contention. Eastern figures the smaller the tax increase, the less pressure there will be to roll back a controversial tax leasing provision that will save the company $100 million over the next five years.

In churches and synagogues around the country last weekend, the Interreligious Emergency Campaign for Economic Justice urged worshipers to telephone their congressmen and oppose Michel-Latta, the Republican plan.

The reason: it cuts more deeply into basic food-and-shelter programs for the poor than the budget plan adopted last week by the Republican-controlled Senate.

This is budget week in the House, and under the procedures that have prevailed for the last two years, the members are doing a year's worth of legislating in just a few days. In the same few days they are feeling a year's worth of pressure; every interst group in town has its shock troops on Capitol Hill.

This year's battle lines are roughly the same as last's, although there are some notable defectors, strays and sideline-sitters. If anything, the economic hardships of the past year appear to have made the social program groups better organized and the business groups more fragmented, but whether that will make any difference in the final outcome, no one is sure.

"Right now, the signs don't look too good," said Paul Kittlaus, chairman of the steering committee of the interreligious group that was formed in January to fight the battle of the budget under the slogan, "The Poor Have Suffered Enough."

Kittlaus' group is one of four broad-based pro-poor budget coalitions, encompassing thousands of local social service groups, that are trying to pick off "Boll Weevil" or conservative Democrat and "Gypsy Moth" or moderate Republican congressmen from the coalition that produced such sweeping budget victories for the White House last year.

"More and more churches have felt the impact of the first round of budget cuts," he said. "We are getting people showing up at our front doors and our back doors looking for shelter. Our food lines are doubling, tripling. We want to get that story out."

It is. Yesterday, for example, the northern New Jersey district office of Republican Rep. Harold C. Hollenbeck reported receiving 70 telephone calls on the budget, 69 of them opposed to Michel-Latta, which would cut low-income housing by $22 billion next year, food stamps by $5 billion over three years, employment and training programs by $1.5 billion over three years, and phase out all funding for legal services over the next three years.

"Obviously they're a lot better organized this time around," said a spokesman for Hollenbeck, who added that the congressman has not yet made a final decision on the budget.

No matter how effective, the grass-roots lobbying blitz has not insulated the defenders of the poor from having to face hard tactical choices as they follow the inside maneuvering of the floor debate.

The chief dilemma yesterday, for example, was whether to support Democratic-sponsored amendments to Michel-Latta that would increase funding for Medicare and education programs. On the one hand, they would make the enemy's bill less hard to take; on the other hand, they might increase the chances for passage of a basically unacceptable piece of legislation.

"We argued all morning over how to handle the amendments and couldn't resolve it," said Kittlaus, who said different groups in his coalition will go different ways. "But basically, everyone's message is that Michel-Latta is not acceptable no matter how . . . sweetened."

That is the same message, curiously, being delivered this week by the National Association of Home Builders, an aggressive business group that was firmly in Reagan's corner during last year's budget battling.

The basically conservative home builders were anxious to support Michel-Latta, but only, if it provided for funding levels that could accommodate the pending programs to shore up their industry, floored by the recession.

The White House claimed it did provide funds; the home builders were never persuaded, and on Monday night their president, Fred Napolitano, telegrammed all 435 House members that a vote for Michel-Latta would make "meaningless" the 349-to-55 House vote two weeks ago in favor of the housing stimulus program.

"The home builders are jumping in on this one with hobnailed boots, and it's got the Republicans worried," said Rep. Les AuCoin (D-Ore.), who helped lead a Democratic initiative in support of the housing plan.

But if the defection of the politically influential home builders was welcome news to Democrats, it was drawing nothing but jeers from other business lobbyists.

"They're the greediest industry in the world," said John J. Motley, head lobbyist for the National Federation of Independent Businessmen (NFIB), which represents more than a half million small businesses. "Our members are suffering just as much as the home builders are, and we're not asking for any bailouts."

Such tensions reflect a new fact of life among business lobbyists: last year's solid phalanx of business support for Reagan's budget proposals has proven to be a short-lived phenomenon. Indeed, even NFIB is opposing Michel-Latta, claiming it strays from the tax-cutting, deficit-lowering posture that is the heart of Reaganomics.

"We're catching some heat from the White House right now, but I think the rest of business wishes they were where we are," Motley said. "We haven't abandoned the president's program; the president has."

Motley's group supported a balanced budget amendment offered by Rep. John H. Rousselot (R-Calif.) earlier this week. Once that failed, it started working to defeat all the other alternatives, hoping to get a better bill in the reconsideration that would follow.

Meanwhile, the other major business groups, Chamber of Commerce, Business Roundtable, National Association of Manufacturers, are behaving in more conventional fashion and supporting Michel-Latta. But, claims Motley, "not with much enthusiasm."