The U.S. Postal Service asked a federal judge yesterday to block Larry Flynt from sending his Hustler magazine to 56 members of Congress who were mailed free copies 17 months ago and did not like what they saw.

The request is based on a federal law permitting citizens to ask the Postal Service to halt mailings they find "erotically arousing or sexually provocative," according to government papers filed in U.S. District Court here.

Several members of Congress denounced the publisher's "smut mailing list" as a "sick publi- city stunt." Sen. Charles E. Grassley (R-Iowa) said he was going to send Flynt an annual subscrip- tion to the magazine Christianity Today.

Then-Sen. Roger W. Jepsen (R-Iowa) termed Flynt's mailing "an effort to promote his dirty magazine."

After Flynt mailed the first of two issues, about 60 members of Congress notified the Postal Service that they wanted the mailings stopped. Some of them no longer are in office, leaving 56 named in the suit filed yesterday.

After a second issue of Hustler was mailed to Capitol Hill, postal officials initiated a formal complaint against Flynt. Yesterday's request for an injunction is a formal attempt to enforce a finding by a postal hearing officer last year that the mailings violated federal law, according to court papers.

Flynt, in a lawsuit filed last year against postal authorities, defended his actions as "exercising my First Amendment right to express my political and social views to public officials."

"It's an attempt to express Flynt's and Hustler's social and political views, the way you'd normally send materials to senators and congressmen," David Kahn, the magazine's president and gener- al counsel, commented in a telephone interview yesterday from Los Angeles. "They don't have to read it."

"It might be a different issue if it were going to their homes," Kahn said, "but it's not."

Kahn said the magazine no longer is being sent to Congress' offices, either.

Royce C. Lamberth, chief of the civil division of the U.S. Attorney's office, said the government will seek to have Flynt's lawsuit dismissed on grounds that it was filed before the administrative process was complete.

In a letter to all members of Congress with the first mailing, in September 1983, the flamboyant Flynt said he was "as committed to my pornography as the pope is to his celibacy, so the quality of Hustler will never be compromised."

The law prohibiting such mail- ings applies to materials that, in the recipient's view, include a "pandering advertisement," according to the government's court papers. The copies of Hustler contained advertisements for subscriptions to the magazine, the Postal Service said.

"If he [Flynt] wants to write a letter," said assistant U.S. attorney Lamberth, "he still can."