Senate Republicans yesterday began a filibuster against public financing of Senate general election campaigns, which President Carter supports.

Discussion of the bill is expected to last all week and perhaps several weeks, with cloture attempt (requiring 60 votes to limit debate) on Friday, and several times next week if that fails.

Republicans have lots of complaints against the bill, but one of the main ones is their fear that it would help Democratic candidates more than Republicans, giving the Democrats a permanent edge in Senate races and making it unlikely that Republicans would ever again gain control of the Senate.

Senate Minority Leader Howard H. Baker Jr. (R-Tenn.) said yesterday that the bill would be "devastating on Republican prospects."

Sen. John G. Tower (R-Tex.) said recently, "It is designed to establish the Democratic Party's primary as the first (official) state political party in our history." He added, "It is clear their objective is to maintain (their) majority status at the expense of Republicans."

These charges were strongly denied yesterday by Fred Werthiemer spokesman for Common Cause, one of the bill's most ardent supporters.

"They are misreading how this is going to work," he said. Wertheimer said the bill would increase the chances of challengers and "outs" by guaranteeing them public funds with which to run, while at the same time reducing the corrupting influence of special-interest donors who often expect favors in return for the money they give.

The bill applies only to general elections for the Senate, not to primaries. It provides that a candidate of a major party can receive up to 62.5 per cent of his or her campaign costs from the Treasury, provided the candidate agrees to a spending limit based on state population. The limit would be $250,000 plus 10 cents for each person of voting age, which currently works out to $532,000 for Maryland, $600,000 for Virginia and $1,688,000 for California.

Republicans believe the bill would help Democrats in two ways.

It would help incumbents (and the Democrats have many more incumbents) by adding to their existing advantage in publicity, congressional staff and other perks a guarantee of a minimum of financing for their campaigns.

At the same time, Republicans contend, the bill would do nothing to offset substantial amounts Republicans believe labor unions spend in indirect aid to Democratic candidates - such as get-out-the-vote campaigns, registration drives in predominantly Democratic neighborhoods, and the like.

None of these activities is counted as a direct contribution to a candidate as long as the union conducts them independently, even though they help Democrats most, Republicans [WORD ILLEGIBLE] They estimated in their minority views on the bill that unions spend $8.5 million for Carter in 1976 by these methods and could do so to congressional candidates, too.

Wertheimer contended that the bill helps nonincumbents more than [WORD ILLEGIBLE] in offiice, giving theme at least a minimum amount of funds with which to challenge. "Incumbents now outraise challengers 2-to-1, so this bill will actually increase competition," he said.

He also argued that nothing in the bill onhances the power of unions to spend independently.

Asserting that the $8.5 million estimate of union spending is much too high, he said that by guaranteeing challengers at least some funds, public financing would help overcome any independent activities by union or other groups.

"I don't think it hurts or helps any particular party - it just increases capacity to compete," he said.

Baker said he feared public financing as another unwholesome step in making senators "professional legislators," barred from outside earning staying in Washington all year, with their campaign expenses paid - more and more cut off from direct contact with those they are supposed to serve.