Sen. Edmund S. Muskie (D-Maine) said yesterday that the Senate is preparing to "throw the weakest dog to the wolves" in order to appease public criticism of Congress.

He was referring to the fact that a proposed new code of ethics imposes an $8.625 annual limit on a senator's fees for making speeches to public groups, but doesn't clamp any ceiling on dividend and interest income which a senator may receive from a private fortune.

The House has already adopted such a rule for its members.

Muskie contends that the code favors rich senators who can supplement their income by clipping bond coupons while discriminating against those like himself, whose only income, other than their salaries, comes from lecture fees. He wants either to strip the lecture fee limit from the code or apply the same ceiling to dividend and interest income.

In an emotional speech recalling his days as Maine governor a generation ago, he said he had been on the lecture circuit all his public life as the only "clean" way to supplement his income. He said Winston J. Churchill, William Jennings Bryand and other public figures had done the same - Bryan while he was Secretary of State under Woodrow Wilson.

Muskie said the limit on fees from speeches was caused by Senate "panic, generated by the reaction of the public" to the recent boost in congressional pay from $44,600 a year to $57,500.

Muskie said he had little financially "to show for my 22 years in public life", but the proposed code says, "I've used my office to enrich myself".

"If I got $50,000 a year" interest from investment in oil, real estate and ohter properties, "that's all right, but that $1,500 from a college lecture isn't."

"Are lecture fees so much more prone to conflict of interest than investment, income?" he asked.

Earlier yesterday, Majority Leader Robert C. Byrd (D-W.Va.) called the question of limiting a senator's unearned income "a phony issue".

He said there isn't much the Senate can do if one of tis members was born rich, but it can and should put a stop to a senator's "using his position to make money".

Byrd predicted that Muskie's amendments would be defeated, and said he believes the new code is "strong and fair" and should be upheld against amendments.

Jacob K. Javits (R-N.Y.) said the public would consider it a "bail out" by Congrees if the Senate, having received a pay raise, were to lift the limit on fees from speeches.

Gaylord Neslon (D-Wis)., chairman of the committee that wrote the new code, said the Senate had previously imposed $15,000 and $25,000 limits on fees, and lowering it to $8,625 was merely a question of deciding that the line should be drawn lower.

When he noted that Muskie hadn't made any objections on principle when the earlier limits were set, Muskie said, "I was a coward."