The real estate industry's effort to preserve its tax benefits moved into high gear this week amid a flurry of press conferences, studies and congressional testimony.

Virtually every segment of the industry would lose something under the plan put forward by President Reagan, and everyone from resort condominium builders to developers of low-income housing projects was on hand this week to say what a bad idea they think the president's proposal is.

The lobbying has been going on behind the scenes since before the Treasury released its first tax reform proposal in November, but this week the campaign entered a more public phase.

The move comes at a time when the drive for tax reform appears to be losing momentum, and the industry's message to homeowners, tenants and investors is that they would be better off under the current system.

Chief among the adverse consequences of the Reagan plan foreseen by the industry are:

*Higher after-tax costs for home ownership.

*Higher rents for both residential and commercial tenants.

*A worsening shortage of low-income housing.

*A sharp decline in the value of resort property, and recession or depression for those areas of the country whose economies are tied to the second-home market.

*A decline in rehabilitation of old buildings and redevelopment of older urban areas.

*Exclusion of middle-income people from certain types of real estate investments.

At a day-long hearing before the House Ways and Means Committee Tuesday, industry witnesses repeatedly used the words "devastating" and "unfair" to describe the Reagan plan.

Committee Chairman Dan Rostenkowski (D-Ill.) noted at the opening of the session that the various provisions of the plan, "taken together, will have a dramatic impact on the real estate industry." But he cautioned that "many people believe" that the real estate industry employs tax shelters "to try to avoid paying its fair share of taxes."

Industry representatives acknowledged at the hearing and at several press conferences that abuses do occur, but they argued that the overall benefits to society outweigh these costs. Further, several said they believe it would be preferable to amend the present tax code to curb abuses rather than rewriting it from top to bottom.

The studies prepared by and for various trade groups paint a particularly bleak picture of the fate of tenants under the Reagan plan. A team from the Harvard-MIT Joint Center for Housing Studies and Wharton Econometric Forecasting Associates Inc. concludes that rents would increase by between 20 and 24 percent by 1991 over "no tax-reform levels."

This increase, which would result from a dramatic decrease in construction of rental housing and an increased demand for it, would more than wipe out any tax savings that renters would realize.

Since tenants tend to have lower incomes, they spend more in rent than in taxes, according to William Apgar of the Harvard-MIT Joint Center. Thus, "a large percentage change in taxes is more than offset by a small change in rents," he said.

According to a study by the National Association of Home Builders, a tenant earning $15,000 a year pays, on the average, $3,900 a year in rent. Under the Reagan plan, this tenant would see his taxes fall $105 a year -- an amount that would be wiped out by a rent rise of 2.7 percent.

The NAHB study, and one done for the National Apartment Association, which represents owners of rental property, also foresee large rent increases. The NAA's Roger Greer, in testimony before Ways and Means, said that "for the average renter, rents will go up from $350 to $410 per month, while average tax savings would be in the range of $7 to $15 per month."

All the groups note that these increases would not be immediate, but would come about gradually as construction slows and supplies tighten.

The Wharton-Joint Center and NAHB studies also predict a sharp increase in the after-tax cost of home ownership. The Joint Center study puts this increase at "approximately 10 to 12 percent, which would make it even more difficult for a young renter household to purchase a home, thereby increasing demand for rental housing."

Both studies see a fall-off in new housing construction through the early 1990s if the president's plan is adopted.

The proposed limitation on interest deductions for second homes would fall very hard on areas that depend on resort activity, according to the American Land Development Association, a trade group representing developers of recreation property. A study by Data Resources Inc., commissioned by ALDA, predicts an annual revenue loss to the Treasury of almost $1 billion "for the next decade due to depressed activity in the second-home/recreational real estate sector."