The National Park Service issued final, more restrictive regulations yesterday governing protests in Lafayette Park and said it will begin removing the billboard-type signs, large permanent protest displays and other "dumplike" items from the park early next month.

The new regulations, published in the Federal Register yesterday and set to go into effect April 4, restrict both the size and number of protest signs in the park and ban the plywood huts and other structures that critics contend mar the park's beauty and obstruct the view of the White House across the street.

"We believe that the exercise of First Amendment rights is of great importance," Interior Secretary Donald Hodel said in a statement released by his office.

"However, we also believe that reasonable limitations must be placed upon that exercise" to protect the park's attractiveness for visitors, he said.

Under the final regulations, signs placed or set down in the park must be no larger than four feet in either dimension and no thicker than one-quarter inch. A protester may not have more than two such signs in the park at any one time and must stay within three feet of the sign or it will be considered abandoned property and removed.

Hand-carried signs will be exempt from the restrictions, and protest groups, depending on their size, will be allowed to set up temporary speaker or "soapbox" platforms for rallies.

Symbolic structures, such as effigies and coffins, will be allowed in the park if they are hand-carried.

Since their initial proposal last August, the regulations have drawn a flood of positive and negative comments from the public -- generating more mail than any issue in recent memory, according to park service spokeswoman Sandra Alley.

Those who support the restrictions complain that a few demonstrators have turned the park into an eyesore, erecting huge plywood signs along its southern border and leaving trash and personal belongings strewn about. Those who oppose the restrictions say the rules infringe on free speech and ignore the park's traditional history as a protest site.

"The regulations go far beyond what's necessary to maintain reasonable appearance and maintain the integrity of the park," Arthur Spitzer, legal director of the ACLU's Washington office, said yesterday. He said the civil libertarian organization may go to court to try to block the new rules.

Lafayette Park protests, including a continuing 24-hour vigil against nuclear weapons, have increased since 1983 when the federal government, citing security concerns, adopted regulations prohibiting large signs or stationary protests on the sidewalk in front of the White House. On Tuesday, 17 White House protesters who challenged the new restrictions in subsequent demonstrations on behalf of the homeless were found guilty in U.S. District Court of violating the regulations. Judge William B. Bryant sentenced 12 of the protesters, who spent a night in jail after their initial arrests, to the time served. Five others received 30 days' probation. Two other demonstrators have opted for jury trials, set for April 7.