A bill to shore up financially wobbly multi-employer pension plans, already delayed four weeks past a crucial deadline, hit another snag yesterday.

As Aug. 1, the 1974 Pension Security Act began to apply to plans where workers are covered by agreements involving more than one employer. It was feared that many of these plans were in such shaky financial shape they would fold now that their benefits are guaranteed by the federal law from a federal fund. The purpose of the new bill is to eliminate the incentive for employers to abandon these plans by requiring that withdrawing employers pay a fair share of the plan's unfunded liability.

The House passed the bill early in the year, but the Senate passed it only three days before the deadline and added three amendments, firecely opposed by organized labor, dealing with safety inspections and employment rights of minority groups. The house refused to accept the Senate version, and Congress went off on a two-week recess for the Democratic National Convention facing the possibility that some of the plans might fold while they were gone.

Early this week, the House stripped away the three antilabor amendments and sent the bill back to the Senate, Tuesday evening, the Senate agreed to drop those three amendments but added another that stirred fresh opposition in the House.

The latest Senate amendment would exempt a Hawaii state prepaid health care plan from a section of the pension law that preempts all state law in this area. Rep. John Erlenborn (R-Ill.), House Republican specialist on the subject, said this would be first step toward wrecking the business-labor coalition that made the law possible.

Unless the House can argue Erienborn out of his opposition to the amendment or decides to try to run over him today, the bill must now wait until Congress returns Wednesday from its Labor Day recess. Then the Senate could drop the Hawaii amendment or send the bill to a House-Senate conference to settle the differences. No multi-employer plan yet has folded during the four weeks they have been subject to the 1974 law.