A broad-based coalition of consumer, labor and civil rights groups will go to Capitol Hill Tuesday and Wednesday to seek protection for homebuyers from the possibility of runaway payments under the new adjustable rate mortgages.

The new mortgages, approved April 23 and designed by federal regulators to help the troubled thrift industry, could lead to massive foreclosures and economic redlining by some lending institutions unless Congress steps in, the coalition has warned.

"This is not a minor slippage of consumer rights, but an historic and major destruction of the [home financing] system," said Ralph Nader, one of the leaders of the 60-member coalition.

Before the April ruling, lenders generally were required to issue mortgages with fixed rates and unchanging payments. The new adjustable mortgages allow federal savings and loans to adjust interest rates and monthly payments on home mortgages according to the rise and fall of prevailing market rates.

To protect today's buyer, the coalition has proposed a ceiling on the increases in monthly payments. The group said that, in any given year, payments should increase at no more than two-thirds the rate of the average U.S. worker's wage gain for the immediately preceding 12 months.

Other measures recommended by the coalition would forbid rate adjustments more than once a year, require that all adjustable rate mortgages use the same index of prevailing interest rates in making adjustments, and mandate standardized disclosure statements showing interest rates and monthly payments.

The coalition, which will push for those measures in hearings scheduled before a House Banking subcommittee, stopped short of calling for elimination of adjustable rate mortgages. "Some of us feel that the ARMs are here and we will have to live with them . . . but that they shouldn't put all the risks on the homebuyer," said Jim Boyle, director of governmental relations for the Consumer Federation of America.

In illustrating its concern about runaway payments and potential foreclosures, the coalition cited the case of a $50,000 mortgage made in January 1978 with an initial interest rate of 9.15 percent, which would have climbed to 17.39 percent by January 1981 if it had been based on an adjustment tied to six-month Treasury bills. Nader said the monthly payment under those circumstances would have risen from $408 and $722.

Martin Sloane, general counsel for the National Committee Against Discrimination in Housing, predicted that lending institutions operating under the adjustable rate mortgage rules will become more conservative and restrictive, "shutting out many minority families and women -- the traditional victims of discrimination -- from the opportunity to obtain a mortgage."

He said the mortgages also will "encourage redlining of older urban neighborhoods, which the lender may believe will appreciate less rapidly than average."

Officials of the Federal Home Loan Bank Board say they have been and continue to be "sympathetic to consumer concerns" about adjustable rate mortgages. In a prepared statement, the board said, ". . . We believe our regulations promote the long-term availability and affordability of mortgage credit while allowing borrowers and lenders the freedom to fashion loan contracts according to their own preferences."