Michael S. Gordon, one of the principal architects of the Employee Retirement Income Security Act, died of pneumonia Sunday in Washington. He was 70. Mr. Gordon served on the President's Committee on Corporate Pension Funds in 1965, and as special minority counsel for pensions to Sen. Jacob Javits, R-N.Y., on the Senate Labor Subcommittee. After leaving Capitol Hill in 1976, Mr. Gordon set up a legal practice in Washington representing small business employers, multiemployer pension funds, participants and not-for-profit organizations. Funeral services were held Wednesday in Washington.