A House panel on Tuesday amended President Bush's savings and loan bail-out plan to ensure that companies which bought failed S&Ls with federal aid last year do not suffer any losses if the assistance is cut off.

But it rejected an effort by liberal Democrats to make both S&Ls and commercial banks reflect on their books the market value of real estate and Third World loans whose value has declined substantially because borrowers are not repaying them.With a two-month honeymoon disintegrating into a kitchen squabble over who takes out the trash and whose friends get invited to supper, the House Banking Committee's financial institutions subcommittee began tackling the most controversial issues in Bush's $90 billion bailout proposal.

On a 31-14 vote, the panel rejected an amendment by Rep. Joseph P. Kennedy II, D-Mass., to make financial institutions list loans as assets only at the level for which they could be sold to others, rather than their original value when issued.

"There's no reason why banks and thrifts cannot be held to the discipline of the market and not hold on their books loans at values which are greatly in excess of what they're worth," Kennedy said. "That's why we are in the trouble that we are today."

Much of the magnitude of the S&L bailout has been blamed on congressionally approved accounting practices that allowed thrifts to effectively hide from regulators the deterioration of souring loans in their portfolios.

"We keep hearing about the need for certainty and stability," said Rep. Bruce Vento, D-Minn. "This would formalize that process. If you want to get tough, this certainly gets tough."

Critics, however, contended that such a radical change in financial accounting practices might hurt both banks and S&Ls dramatically.

"If we were in a new world and starting from scratch, it would be appropriate," said Rep. Cliff Stearns, R-Fla.

The panel approved on a 35-7 vote a measure by Rep. Doug Barnard, D-Ga., that would protect holding companies that bought ill S&Ls last year with the promise of government aid from having to absorb the costs if those insitutions fail because the assistance is cut off.

Barnard said the measure was aimed at preventing other S&Ls under a holding company's umbrella from also failing because of a government failure to live up to the aid agreements.

But Banking Committee Chairman Henry B. Gonzalez, D-Texas, complained that the amendment would create a large loophole for holding companies to skirt any liability if the once-failed thrifts go under again.

The panel had yet to tackle the much tougher capital standards that Bush and bankers want to place on S&Ls and an off-budget financing scheme that has drawn the opposition of House Ways and Means Committee Chairman Dan Rostenkowski, D-Ill.

To discourage risky loans blamed for much of the current crisis, Bush would require S&L owners to put up 6 percent capital - or $6 of their own money for every $100 they lend - by June 1991. Those who don't could not make additional loans with federally insured deposits.

But the subcommittee's chairman, Rep. Frank Annunzio, D-Ill., and Barnard have an amendment that would require S&Ls to effectively have only 1.5 percent "tangible" capital in relation to total outstanding loans.

Many S&Ls already fail to meet the current 3 percent capital requirement.