President Reagan has belatedly served notice he believes provisions of the voting rights bill the House passed earlier this month are "pretty extreme," and he will seek weekening amendments in the Senate.

An aide said yesterday one amendment under consideration would increase significantly what the government has to prove to find a state or local jurisdiction in violation of the act. It would require the government to prove not only that minority-group members were excluded from public office or denied the right to vote by local election laws but also that the officials responsible for the local laws intended the discrimination.

Opponents say such a change would cripple further efforts to open up all-white city councils, school boards and commissions to minority groups, and that the offering of such a proposal could put Reagan on a collision course with House Republicans who overwhelmingly voted to support the bill as passed.

The administration avoided taking a specific position on the voting rights bill as it moved through the Democratic House; the president contented himself with expressions of generalized support for it. The bill is now expected to have a much more difficult time in the Republican Senate, where conservative Sen. Strom Thurmond (R-S.C.) has not scheduled it for hearings before his Judiciary Committee until January.

Aides said that in addition to the intent amendment the president was considering one on the issue of "bailout": how a jurisdiction might be permitted to exempt itself from the provisions of the law by several years of good conduct.

David Walbert, one of the lawyers who will represent Burke County, Ga., blacks in a voting right case before the Supreme Court early next year, called the contemplated change on intent "really an evil thing. It really does return the law to almost a pre-Civil War state.

"The major problem in the South is the at-large election . . . and it is very difficult to prove intent after 25, 50, even 100 years. As long as you have those [at large elections] in effect, blacks will never be elected. You'd have to be a blind toad not to see how at-large elections affect blacks," he said.

Earlier this month, the House by a lopsided vote of 389 to 24 passed an extension of the 1965 act with a provision stating explicitly that the government need not prove intent to discriminate to find a violation.

Rep. James F. Sensenbrenner Jr. (R-Wis.), one of the co-sponsors of the House bill, said it "was not the intent of the Congress when it passed the act in 1965 and extended it in 1975 and 1980" to require that intent be proved. But the Supreme Court in a decision last year suggested that intent might be required. The new language was offered partly in response to this; it "is supposed to make it crystal clear that if the actual result [of the local voting laws] is discrimination, then they should be knocked down," Sensenbrenner said.

Sensenbrenner added that if the president is able to convince the Senate to go along with him, "I see a very long and difficult conference. I don't see the House caving in on this very critical provision of the bill."

Rep. Don Edwards (d-Calif.), another sponsor of the House bill, said he was stunned that the administration would consider major changes. "This is a very modest, reasonable bill," he said. "It basically extends existing law which is working very well."

The Civil Rights Act specifically spells out that there is no need to prove intent, and until a controversial Supreme Court decision last year, there was no precedent for requiring proof of intent under the Voting Rights Act.

But in a split vote approved by only four of the justices, the Supreme Court found in 1980 that the Constitution "does not entail the right to have Negro candidates elected," and that they city of Mobile, Ala., was not deliberately discriminating against blacks when it enacted an at-large system of electing its commissioners in 1911.

Lawyers say that it is virtually impossible for them to prove intent, even in racial discrimination cases, that it puts them in the position of trying to "psychoanalyze" local officials and that can be very difficult.

Fred Fielding, counsel to the president, confirmed yesterday that Reagan is leaning toward an intent amendment, but he said it is "premature" to predict what the president's recommendations will be until he meets with the Cabinet on the question, probably next week.

"I don't think the president would like to go against the Supreme Court . . .," Fielding said. "In essence, the House bill changes the intent of the Supreme Court."

At a meeting with newspaper editors last Friday, Reagan said that the House "has been pretty extreme in what it's done" and that he hopes the Senate will be more "reasonable."

Earlier this year Reagan said he would like to see the act, which affects nine states and parts of 23 others, expanded to the entire country, but he changed his mind after being told that such an effort would be so cumbersome that it would be impossible to enforce.