The new adjustable-rate mortgages that are expected to revolutionize home buying habits won't have an impact on Washington area home sales for at least two to three months, area lenders said yesterday.

"It will take from 60 to 90 days for institutions to get the proper papers prepared to make these [adjustable] loans," said James L. Harris, president of Washington Federal Savings & Loan Association. Moreover, savings and loans have very little mortgage money available at present to lend to prospective buyers, regardless of the rate they charge or the type of mortgage terms they require, Harris said.

"A person won't find it any easier or any harder to get a loan . . . for several months," he said.

Under the new rule, which officially takes effect Thursday, federally chartered S&Ls will be allowed to adjust the home buyer's monthly mortgage payment up or down, according to general interest rates. Existing home loans, which typically are based on a fixed interest rate and fixed monthly payment throughout the life of the loan, are exempt from the rule.

Lenders say that the improvement in the S&Ls' economic health that the adjustable mortgages are intended to bring ultimately will be good for consumers who want to borrow money to buy houses. But officials also acknowledge that consumers bargaining for an adjustable mortgage will need more sophistication and savvy than they needed in the past for the fixed-rate mortgage.

They said that consumers now negotiating home loans generally won't be affected by the rule change."Our policy would be to close [the loan] with anyone with an outstanding commitment," said Thomas J. Owen, chairman of the board of Perpetual American Federal Savings and Loan Association.

However, buyers who don't already have a written agreement for a fixed-rate mortgage may have no choice other than the adjustable-rate mortgage.

The variable-mortgage rule approved Thursday by the Federal Home Loan Bank Board does not apply to state-chartered S&Ls. However, the state agencies normally allow their S&Ls to follow federal institutions.

National banks are already authorized to write adjustable mortgages but are limited to a maximum interest rate increase of two percentage points a year. The federal S&L rule has no limits on interest rate increases.

S&Ls typically provide more than 50 percent of the money for home mortgages.

The adjustable-rate mortgage, under the new rule, can take almost any form, depending on the policies at the individual institution. But lenders said yesterday that one possibility now being considered would provide for the monthly interest to rise and fall in keeping with market rates while the monthly payment remained the same. The extra interest owed for those months of higher interest rates would be added to the principal and the life of the loan extended until that extra interest was paid off. For example, the home buyer might take out a 40-year loan amortized over 30 years. The monthly payments for the 30 years then would be the same. If any additional interest were owed as a result of higher interest rates during the first 30 years, it would be paid off during the last 10 years. If interest rates should drop during those 30 years, so that the borrower overpaid on the total interest due, the overpayment, depending on how the contract is written.

That is the type of adjustable-rate mortgage that officials of the U.S. League of Savings Associations expect to dominate the market at least initially as S&Ls struggle to win consumer acceptance of the new concept.

"We expect that because that is what the market will require," said Jim Christian, a league economist.

Meantime, the lack of mortgage money continues to be the primary problem for lenders and borrowers.

Washington area S&Ls made only 14,767 residential loans during 1980 -- down from 19,204 in 1979 and from 21,433 in 1978. The dollar amount of the loans also has declined. In 1980 the institutions lent $1.044 billion, compared to $1.279 billion in 1979 and $1.271 billion in 1978.

And the interest rate for the rate loans that are available is 15 1/2 to 16 percent.

S&Ls believe the new mortgages will help stabilize the institutions and create an environment in which more loan money will be available.

One home seller, who has had his Silver Spring house on the market since November, said he would welcome "ANYTHING" that would free up mortgage money and ease the personal financial strain of home buying.

"We've explored virtually everything possible to sell the house," said Barry Friedman, whose four-bedroom Colonial in the Bel Pre section of Silver Spring is being offered at $119,950, with owner financing.

Friedman listed the house with a realtor for three months, reduced the price $5,000 during that time and finally took over its selling himself in January. He dropped the price another $10,000 over the months, still without any firm takers.

"When push came to shove, a mortgage rate of 15 percent made people shy away, particularly when they figured out the monthly payments," said Friedman, who is convinced "the buying public is disheartened by what's going on."

"Whatever can be done to decrease the monthly payments, I'd be in favor of," Freidman said. "People just don't have enough take-home pay to cover that."

However, the prospect of adjustable rates brought a mix of reactions among Washington area realtors.

"I just see it as another tool at our disposal, but it's too early to tell if it will even be used," said one official at Shannon & Luchs, the largest realty firm in overall volume in the metropolitan area.

Dale Denton, president of Dale Denton Real Estate Inc., said his firm had made use in the past of variable interest rate loans and had found they stimulated selling.

But Richard Metzler, owner of Metzler realtors, remained dubious.

"I think anybody would be a dog-gone fool to sign anything like that," he said. "Maybe I'm just too old or conservative, but I'd be amazed if people rush in to get these loans."

The adjustable-interest rate loan has already been tried out in California, whose savings and loan institutions have been making them in some form for five years, and in Texas, which for a year has made loans using a variable interest rate system virtually identical to the one announced at the federal level.

"The reception has been quite good . . . ," said Den Cannon, executive vice president of the California Savings and Loan League.

However, the limitations placed on making such loans to date have tended to make them more attractive to the consumer that the lending industry, Cannon said.

In Texas, Durward Curlee, executive vice president of that state's Savings and Loan League, said restriction-free variable interest rate loans have been in wide use, especially by developers and lending institutions in large cities.