On the eve of the convention that will name him as the Republican contender for the presidency, Ronald Reagan said today he expected the Soviet Union to try to help President Carter defeat him in November.

In an interview at his California home taped for showing Monday night on CBS-TV's "60 Minutes," Reagan said, "I think very definitely the Soviet Union is going to throw a few bones to Mr. Carter during the coming campaign in order to help him continue as president.

"I would be very worried about me if the Soviet Union wanted me to be president."

The president's press secretary, Jody Powell, said Carter would have no comment on Reagan's remarks. Powell was with the president in Georgia, where the president is vacationing on a coastal island.

Reagan is to arrive here Monday to join the 1,994 delegates who will officially nominate him Wednesday as the GOP standard-bearer and the thousands of visitors and reporters who have streamed here into this auto capital.

The secret of Reagan's vice presidential choice remained intact, but there was growing sentiment among the delegates for adding Reagan's most persistent challenger in the primaries, George Bush, to the ticket.

The convention rules committee cleared away a tangle of procedural questions with little troubles, as the delegates found their way to hotel rooms scattered from Windsor, Canada, to Ann Arbor, Mich., and Toledo, Ohio, and dressed for the first big social event of the week -- a $1,000-a-person GOP fund-raising gala.

Except for Reagan, the cast of chara cters for the convention was on hand, led by former president Gerald Ford and the half-dozen men considered contenders for the vice presidential nomination.

There was little real news during the day, except for the comments Reagan made to CBS' Mike Wallace in his "60 Minutes" taping.

The former California governor, a consistent critic of Soviet expansion, said he thought the Kremlin would like to keep him out of the White House "because, for one thing, I oppose a SALT II treaty," such as the one the Carter administration negotiated last year but then asked the Senate to postpone considering because of the Soviet invasion of Afghanistan.

Reagan insisted that if he became president, "I would sit down . . . with the Soviet Union for as long as it took to negotiate a legitimate arms reduction, but I cannot support a supposed arms limitation treaty that augments the nuclear weapons on both sides."

The prospective nominee said the Soviets were wrong if they thought him "trigger-happy. But I am also aware that vacillation, weakness, on-again, off-again policies such as this administration has displayed can back us into a war."

Reagan has often suggested that it was a lack of resolve on Carter's part that encouraged Soviet aggression in places like Afghanistan. Last April, in an appearance before the American Society of Newpaper Editors convention in Washington, Carter implied that Reagan was playing the Soviets' game in making such charges.

"I think the people in the Kremlin would agree completely with what Mr. Reagan has said -- that the invasion of Afghanistan was not the fault of, nor the responsibility of, President Brezhnev and the Politburo, but was the responsibility of the president of the United States," Carter said.

"That's obviously a ridiculous claim and could only damage our own nation's prestige, coming from a responsible person, and help the Soviets in their claim that they had adequate provocation from this country to take this unwarranted action," Carter added.

While everything appeared primed for an enthusiastic welcome for Reagan and an untroubled nomination Wednesday night, echoes continued to rebound from last week's platform disagreements.

Former president Ford said he thought the call for an antiabortion constitutional amendment and the failure to reendorse the Equal Rights Amendment "will not gain any votes and will probably lose votes."

Ford said on "Issues an Answers" (ABC, WJLA) that he could "basically support the platform" but had "a strong commitment to ERA" and thought the abortion question should be handled through legislation, rather than a constitutional amendment.

Supporters of the ERA are planning a march and demonstration Monday, and some pro-ERA Republicans have been invited to meet with Reagan Tuesday. But no floor challenges to the two sections of the platform are expected, and two of Reagan's top strategists today defended the political wisdom of the planks.

sen. Paul Laxalt of Nevada, the Reagan campaign chairman, said on "Face the Nation" (CBS, WDVM) that the decision to drop the Republicans' past support of ERA "is a wash" politically, adding that "I don't see any indication that the general public is all that involved" in the issue.

As for the antiabortion amendment, Laxalt conceded that "most people probably oppose an amendment" but said "those people who feel strongly . . . that abortion permissiveness is wrong" are more likely to make their voting decision on the basis of that issue.

Ed Meese, Reagan's issues chief, said that even without ERA, the GOP plank "is the strongest endorsement of equal rights for women in any party platform in 40 years."

The issue of the party chairmanship, which stirred a fuss last month when conservatives tried to persuade Reagan to replace Bill Brock as head of the Republican National Committee came up again today -- but was quickly handled.

At a meeting of the convention rules committee, there was unanimous support for a change that will require Brock to face reelection next January, rather than holding office until January 1982.

The new rule establishes a fixed two-year term for national chairman, beginning next January. Brock will be reelected at the end of the convention with Reagan's support, but the nominee, if elected, will have the option of replacing Brock after the election.

The rules change was promoted by conservative members of the national committee, but Brock passed the word that he endorsed the idea, so there was no fight.

The convention rules committee overruled a decision made last week by the party rules committee to drop from the national executive committee representatives of black, hispanic and other ethnic groups who have held ex-officio positions on that panel.

The party rules committee voted to keep the chairmen of the National Black Republican Council, the Republican National Hispanic Assembly, the National Republican Heritage Groups Council and several other groups on the RNC executive committee, a panel that can act for the whole committee between its meetings.

"The Reagan folks decided they didn't need a fuss with the blacks and Hispanics," one senior RNC official said, explaining the turnabout.

The rules committee also voted yesterday to require that all three members of the national committee from a single state approve before the RNC gives any money to a candidate running in a contested Republican primary in that state.

Debate on this proposal revealed sharp divisions on the desirability of allowing the RNC to pick a favorite in state primaries. The proposal that was adopted -- in effect a move to limitthe RNC's discretionary authority to give money to candidates of its choosing -- carried by a vote of 50 to 39.