If you've heard rumblings that Congress is going to ban assumptions of low-interest-rate mortgages this year, rest easy.

The chances of that happening are growing fainter every day -- despite tough lobbying on Capitol Hill by the nation's savings and loan industry.

It's true that the chairman of the Senate Banking Committee, Jake Garn (R-Utah), is pushing a major bill that would override state laws limiting lenders' rights to ban mortgage assumptions.

It's also true that President Reagan's blue-ribbon Housing Commission is plugging for the same federal override power. Also, the Department of Housing and Urban Development is thinking about inserting controversial "due on sale" (nonassumption) clauses in future FHA mortgages.

But all the Republican and industry political muscle at work on this issue won't be able to deliver legislation to the White House by the fall.

There are two key reasons why.

First, 1982 is a congressional election year. No incumbent in his or her right mind wants to come out swinging against prospective home buyers and sellers before November. Most senators -- such as Garn -- aren't up for reelection, but all 435 members of the House of Representatives have to face the voters in November.

Garn may be able to persuade his committee members to pass the anti-assumption bill later this spring, and perhaps even convince the full Senate to come along before the election.

But he'll be up against a brick wall in the Democratic-controlled House, even among members of his own party. Mortgage assumptions are an emotional, gut-level economic issue in dozens of congressional districts right now. Legislatures or courts in 17 states have acted to restrict lenders' powers to ban assumptions of low-rate loans.

The depressed real-estate market in most of the 50 states depends on so-called "creative" financing for the bulk of its volume, and mortgage assumptions are often vital ingredients in those transactions.

"Take away people's ability to pass on their low-rate, long-term mortgages when they go to sell their home," says a California attorney active in that state's political fight over assumptions, "and you've effectively prevented them from selling their homes. It's as basic as that."

No member of Congress is going to be reelected on an anti-consumer, pro-lender plank on mortgage assumptions -- not in the middle of the worst real-estate recession in three decades.

There's a second reason why home sellers and buyers can breathe easier about Capitol Hill's mortgage plans. Congress -- like most of us -- loves an opportunity to pass the buck.

The Supreme Court has just handed Congress precisely that opportunity. The court agreed in late January to hear arguments in a California case, Fidelity Federal Savings and Loan v. De La Cuesta.

The case involves a challenge by a federally chartered S&L in a suburb of Los Angeles, against California's statutory prohibition of due-on-sale clauses. The S&L maintains that as a federally regulated lending institution, it is not subject to state laws regarding mortgages.

The borrowers insist that due-on-sale clauses are illegal restraints on trade, regardless of whether the Federal Home Loan Bank Board sanctions them (which it does).

The high court will take up the case in November, and probably render a decision sometime in the spring of 1983. There's no predicting which way the Court will go on the issue, but the ruling is certain to be a landmark for consumers and lenders. It should help settle, once and for all, whether the anti-assumption language contained in most conventional home loans written since the early 1970s can be modified or negated by state legislatures or courts.

Meanwhile, the fact that the Supreme Court has jumped into the mortgage-assumption controversy gives congessmen a convenient way to jump out. They'll leave the whole problem on the court's doorstep.

The odds are heavy that Congress will do that without a blink. So home sellers and buyers -- especially in states where the court systems are clogged with fights over assumptions between lenders and borrowers -- can stop worrying about intervention from Washington.

That is, until next spring, when the court may change the rules of the game permanently