The Federal Home Loan Bank Board announced a $630 million aid package yesterday that could generate as much as $4 billion to bolster the ailing savings and loan industry. In another action with the same objective, it authorized S&Ls to begin making mortgage loans whose rates vary with inflation.

Jonathan Lindley, executive vice president of the National Savings and Loan League, hailed the action, saying "the bank board is clearly recognizing that the unsettled economic environment, characterized chiefly by sustained high rates of inflation, has severely constrained the ability of S&Ls to earn a reasonable return and to continue supplying homebuyers with mortgage credit."

According to the bank board, the number of federally chartered S&Ls operating in the red during the second half of 1979 increased by 42 percent from the first half to 266 out of 4,100, and the number is expected to rise again in the 1980 first quarter.

S&L losses for this year -- the worst for housing since World War II, in the words of bank board Chairman Jay Janis -- are expected to run into the billions of dollars if current high interest rates persist. This is the third time since last November that the bank board has acted to make funds available to thrifts.

The bulk of the latest rescue effort -- $400 million -- will be in the form of double dividends, paid quarterly instead of at yearend, from the 12 regional Federal Home Loan Banks in which S&Ls hold stock. Collectively they have $6 billion in capital which the bank board feels should be tapped in this crisis.

In addition to the 400 million, the regional banks have pledged $140 million from their surpluses, and $50 million each from special reserve accounts and dividends of the Federal Home Loan Mortgage Corp., a government-chartered, secondary-mortgage-market company. Janis emphasized that none of these are appropriated funds.

Out of the $630 million, $100 million initially will be earmarked for a targeted advances program (TAP) for those thrifts in the most trouble. The TAP funds will be used to subsidize loans to S&Ls at 2 1/2 percentage points below market rates.

To participate, associations must have had operating losses for at least three consecutive months in 1980 and have a net-worth-to-savings ratio of 2.5 percent or less. (The required ratio for financial soundness is about 4 percent.) S&Ls whose woes result from poor management won't be eligible.

Each association will be able to borrow up to 10 percent of its total savings, a provision that could pump up to $4 billion into thrifts. (The subsidy also could be used to reduce interest rates on existing loans.) Virtually all of this money will go to help S&Ls improve their balance sheets, with little or none going for mortgage loans. The advances program goes into effect immediately; the first double dividends will be paid in June.

The bank board's other major action yesterday was to issue its final proposed regulation on renegotiated-rate mortgages (RRM). The interest rate on this new type of loan is subject to change every three to five years. It rises or falls within set limits according to prevailing market rates.

In welcoming the action, U.S. League of Savings Association President Edwin B. Brooks said "given today's economic situation and the government efforts to puncture the inflationary bubble which makes current home financing costs so extraordinary, many consumers will welcome the possibility of lower rates three or five years hence."

Although the industry long has favored the RRM as a means of increasing the yields on loan portfolios to bring them closer to the high rates paid on savings certificates, consumers generally have been opposed. Most fear giving up the inflation-fighting security of a fixed monthly mortgage payment.