The Maryland Senate, see thing with anger over public criticism by Common Cause lobbyists yesterday severely weakened an ethics bill supported by the "citizens' lobby" by watering down a provision to tighten financial disclosure requirements for public officials in Maryland.

By voting to delete a portion of the bill requiring officials to disclose the source an damount of their annual income, the Senate left the legislation weaker than the current disclosure laws and removed a major element of the measure, which was drafted with the help of Common Cause.

"It hurt us badly," said Sen. John Carroll Byrnes (D-Baltimore), prime sponsor of the bill. "The public has a right to know the extent and nature of any conflict of interest by a member of the legislature. The only way they'll have that chance is through financial disclosure of income."

The amendment which passed by a one-vote margin, drew the support of several senators who were criticized two days ago by Common Cause's chief lobbyist for "breaking a promise" to support ethics legislation requiring financial disclosure for local officials as well as for state officials.

"It would be fair to call my vote (for the amendment) a protest vote," said Sen. Clarence M. Mitchell III (D-Baltimore, who was one of the senators criticized by Common Cause. It makes me want to be against the whole bill. The arrogance with which they browbeat people turns legislators off."

Sen. Victor L. Crawford (D-Montgomery), who also was criticized by Common Cause, did not vote on the amendment. He said afterward, "You try to help these people and then they stab you in the back. You can't win with these people even if you play ball with them."

Common Cause lobbyists have been criticized before for compromising the group's effectiveness in the Maryland legislature by making harsh statements about legislators who don't support their proposals. One of the cardinal rules here is not to "spot" a legislator for a contrary vote.

At the same time, many lawmakers who own their success to old-fashioned political machines are said to be using their distaste for Common Cause's unconventional tactics as an excuse for killing the reform measures. Maryland was one of the last states in the country to adopt an open-meetings bill.

The ethics bill is designed to tighten financial disclosure and conflict-of-interest laws for public officials. In the wake of numerous political scandals, including last summer's (political corruption conviction of suspended governor Marvin Mandel).

The amendment approved by the Senate yesterday was sponsored by Sen. Jerome F. Connell Sr. (D-Anne Arundel), who argued that disclosure of the amount and source of an official's income could create an invasion of the official's privacy "without serving any purpose."

The move to delete that provision from the bill was called a "step backward" by the bill's sponsors because it leaves the measure weaker than current laws, under which an official must reveal any income from a firm that does more than $10,000 a year of business with the state.

The bill, which was originally sponsored by a majority of Senate members, survived several other crippling amendments, including an apparent move to "weigh down" the legislation by extending it to judges, who are now covered by their own code of ethics.

Last week, the Senate deleted another major portion of the bill requiring local subdivisions to enact ethics laws covering their own officials by the end of 1979. Yesterday, another amendment was passed, restoring part of that requirement by mandating that all subdivisions with populations larger than 10,000 enact ethics laws.

The political significance of ethics legislation in this election year inspired a heated exchange yesterday between acting Gov. Blair Lee III, whose own bill was defeated in a Senate committee, and Senate President Steny H. Hoyer, a sponsor of the measure now being debated on the Senate floor.

Hoyer and Lee are rivals in this year's gubernatorial election.

At this weekly press conference, Lee accused Hoyer of "playing games" by introducing his own measure instead of collaborating with the administration. "It was a great mistake to introduce a competing bill," Lee said, explaining that the duplication ended up doubling the legislature's work.

Hoyer answered Lee in kind as he held what was billed as the first of many press conferences by the General Assembly's presiding officers. He said Lee "is incorrect" if he thinks that Hoyer played games with the bill. Hoyer added that Lee had never asked legislative leaders to collaborate with him in the drafting of the bill.