Three Republican members of the U.S. Conference of Mayors criticized D.C. Mayor Marion Barry yesterday for waiting until a week before the election to release a conference report that is highly critical of the Reagan administration and contains spending proposals at odds with conference policy.

Mayor Hernan Padilla of San Juan, Puerto Rico, president of the bipartisan Conference of Mayors, issued a statement warning that "it would be misleading to suggest" that the report, calling for $49 billion in additional federal spending for major cities, reflects the views of the members.

"I and many other mayors will not agree on a proposed $49 billion spending program for urban areas," Padilla said, adding that the report failed to present "many of the positive effects" of Reagan administration policies."

Mayor Robert Isaac of Colorado Springs and Mayor William J. Althaus of York, Pa., held a press conference at the Conference of Mayors headquarters here to blast Barry for using his position with the conference to try to embarrass Reagan.

"As an active member of the conference since 1979, I can say without hesitation at all that this particular activity constituted the most blatant use of the Conference of Mayors by a member or by a group of members for purely partisan political purposes," Isaac said.

Barry, chairman of the conference's Special Committee on a National Urban Policy, declined to comment on the criticism yesterday.

Annette Samuels, Barry's press secretary, said it was her understanding that the draft report had been circulated among members of other conference committees prior to its release.

"It the report wasn't issued as a reflection of conference policy," Samuels said. "It was issued as a report from the committee."

The 420-page report, including a preface signed by Barry, was released at a press conference Tuesday at the District Building.

Barry was the only member of the Conference of Mayors who was present.

The study included a proposal to create a National Urban Development Bank that would pump a total of $20 billion in working capital into urban areas over four years. The report also rejected Reagan's proposal for creating special urban enterprise zones in low-income areas, describing it as "a poor substitute for the massive policy shifts in recent years away from cities."

Yet when the Conference of Mayors met in Philadelphia in June, a resolution pushed by Barry in favor of the urban bank concept was tabled, while another resolution backing Reagan's enterprise zones was adopted.

"I don't care what Barry says and he doesn't care what I say, but it the report is not conference policy," said Althaus, who introduced the enterprise zone resolution at the annual meeting.

Althaus and Isaac complained that Barry's urban policy committee should have finished work on the report last September, or at least in time for it to be reviewed by conference members in June.

"With virtually no warning we got this a week before the election and they say here's the conference policy," Althaus said. "No way."

The Conference of Mayors, which represents between 500 and 600 large cities, is dominated by Democratic mayors, who make up about 65 percent of the membership.

While the organization has lobbied hard for additional aid to the cities, the membership in recent years had taken a more cautious approach to federal budget matters and refrained from calling for big new spending programs.