Amid complaints that Washington has gone "ethics happy," a Senate committee indicated yesterday it will let Office of Management and Budget Director Bert Lance out of his pledge to sell his bank stock by Dec. 31 if he will steer clear of federal baking policy while he owns it.

Under gentle but firm prodding from the Senate Governmental Affairs Committee, the financially troubled budget chief said he would work out an agreement with the Senate Banking Committee by early next week on guidelines for "insulating" himself from bank-related issues.

But Lance, acknowledging he may have violated an earlier promise to stay out of banking matters, conceded he's not sure how all potential conflicts of interest can be avoided.

"I guess everything you do and say presents the opportunity for a potential conflict of interest . . .," said Lance, who agreed to the Dec. 31 divestiture date last January as part of President Carter's preemptive strike against conflicts of interest in government. "I don't know how to deal with that, and it worries me very much."

It worried the committee, too, but in different ways.

"I think we've gone completely ethics happy around here. We've gone crazy," said Sen. John Glenn (D-Ohio), who complained that good people are avoiding government service because it's "gotten so tedious trying to be Simon-pure on every bloomin' thing."

"What bothers me," said Sen. William V. Roth (R-Del.), "is to make the overpromises and then, when the going gets rough, to ask for an exception."

Said Sen. H. John Heinz (R-Pa.): "If you overpromise on ethics, you can get in deep trouble. Mr. Lance, in his zeal, has overpromised."

Lance's difficulties stem from the fact that the price of National Bank of Georgia stock has plummeted since he borrowed $3.4 million to buy shares now amounting to about 200,000, or roughly 16 per cent of the bank's total.

He testified yesterday that he would lose about $1.6 million if he were forced to seel the stock now.

Earlier this week, President Carter proposed that Lance keep the stock and turn it over to a corporate trustee for eventual disposal so as not to impose "an undue financial burden" on Lance or the bank by insisting sale by a specific deadline.

Lance is not legally required to get a waiver from the committee but said yesterday he felt a moral obligation not to break the Dec. 31 sale agreement unilaterally.

In the same agreement, Lance also pledged to disqualify himself from baking policy while he held the stock. Several committee members, including chairman Abraham A. Ribicoff (D-Conn.), indicated yesterday they felt he had violated the promise bi signing a letter stating administration opposition to a provision of the pending Community Reinvestment Act.

The provision as aimed at ending "redlining," under which financial institutions avoid loans in high-risk neighborhoods. Lance said the letter was prepared by others and he signed it only because he considered it a housing, rather than banking, matter.

"If I violated that pledge - and there is some weight of opinion that I did - than I apologize to this committee and to Sen. Proxmire," said Lance. Sen. William Proxmire (D-Wis.), chairman of the Senate Banking Committee, had charged that the ltter was violation of Lance's earlier pledge.

Lance told Ribicoff's committee that a deputy would handle such matters in the future.

Still at issue is whether, in releasing Lance from his old promise, the committee will attach some strings to force a sale at some future time, as Sen. Jacob K. Javits (R-N.Y.) suggested be done. Javits said the committee shouldn't "sign off completely."

Lance said the matter would be out of his hands and under countrol of the trustee. But, with roughly $373,000 due each year in debt payments, Lance said he was anxious to sell the stock "as soon as practicable."