In the wake of 1976 sex and expense account scandals and the revelations of Koreagate, Congress quickly passed - early in 1977 - a new and stricter code of ethics.

But that was last year. This year the mood of Congress has shifted and that could spell trouble for the "ethics" legislation that remains to be acted upon.

The trouble surfaced last October. Having accepted the new code, which required members to disclose their dinancial dealings and imposed on them a controversial limit on the outside income they could earn, members found, as Rep. David R. Obey (D-Wis.), said, they will still "getting shot at."

The Korean influence-buying investigation was still going on, widening the circle of members it ensnared, and Obey, who headed a commission that wrote the code, said a constant "drip, drip, drip of criticsm" eroded enthusiasm for reform.

When Obey attempted to offer, on Oct. 12, a final commission package dealing with revising the committee system. House administrative practices and discrimination against black and women employes, it was soundly defeated.

House Speaker Thomas P. O'Neill Jr. blamed the defeat on a "blacklash" against reform.

The problem now is that ethics legislation is only about half completed. Several pieces remain to be passed:

The code itself has only been adopted as House and Senate rules. Until it is codified by being passed into law, no civil or criminal penalties can be attached for violating it.

Financial disclosure has not been extended to the executive and judicial branch.

A disclosure bill for persons and groups lobbying in Washington is still pending.

And finally, a related piece of legislation is still at issue - extending public financing of campaigns to House and Senate races as has been done for presidential races.

The Senate passed an omnibus government ethics bill, with financial disclosure for all three branches, last June. The Senate bill also authorizes appointment of a special prosecutor to handle allegations of wrongdoing by the president and other top officials, and bans appointment of prominent presidential campaign aides as Attorney General.

Four House committees have put out bills dealing with financial disclosure and marrying them into one is one of the problems the House faces.

But the greatest problem is strategy and timing to avoid the backlash.

Timing is important because, under the code passed last year, the first filing of House members financial statements will take place on April 30.

Last year, Obey brought up his illfated proposals just one day after the publication on members expense accounts.

Members voted on the measure just as newspapers were reporting on members of Congress who had used their expense accounts to buy liquor for a party, rent a tuxedo and pay bar association dues.

Rep. Richardson Preyer (D-N.C.), chairman of the Select Committee on Ethics, feels it's important to bring the bills to the floor before the April filing date, which is likely to generate more stories on members' financial holdings.

However, other key members are advising the leadership to hold off until August, when the publicity will have died down and the upcoming elections will put more pressure on the members to vote for the measure.

In addition to the timing problem, many members still are incensed over the 15 percent limit that was placed on the outside income members can earn. While that is not at issue in these bills, they still must go through the Rules Committee, where opposition to the income limit is strong, and a move could be made to open up the bills to another vote on the income limit issue.

But Preyer is convinced he can get the bill through intact. "I really don' think the Obey measure was a precedent. That hadn't been voted on before. But here we voted on this and passed it by a substantial margin. I don't think members could reverse that in an election year," Preyer said.

Then too, there is a carrot in this bill along with the stick. Only by passing this bill can members extend the requirement for financial disclosure to their opponents in election campaigns.

A bill tightening disclosure requirements for lobbyists is now being marked up by the House Judiciary Committee, and markups on an even tougher bill will start in the Senate Governmental Affairs Committee soon.

A similar bill died in the closing days of Congress in 1976.

This year, in deference both to the House's anti-reform and anti-regulation mood, the House bill is milder. And in markup last week, even more provisions, believed to put too onerous a reporting burden on lobbyists, were cut out.

Basically the bill seeks to cover all major lobbying groups, and require them to report their expenditures over a certain amount, their lobbying activities and the issues they are working on. It seeks to update a 1946 lobby registration law, which left wide loopholes and included as lobbyists only those groups or people whose principal purpose was lobbying.

Though parts of the bill are opposed by almost every kind of lobbying group, from the American Civil Liberties Union and the Sierra Club to the U.S. Chamber of Commerce the coalitions shift on each provision.

Rep. George Danielson (D-Calif.), who guided the bill through a Judiciary subcommittee, said lobbyists are reluctant to oppose the whole bill; they just want to change portions affecting them. He believes the bill can be passed.

As one member said, "Having required disclosure of ourselves, we're darn sure not going to let the lobbyists off."

Extending public financing to House campaigns will be offered as a floor amendment to a bill making changes in the federal election law and federal election commission practices.

There is practically no change the amendment will be adopted by the House Administration Committee, which handles the election laws, but drafters are working on a version they hope will attract bipartisan support when the election law bill comes to the floor.