A former Grenadian diplomat who was arrested Thursday night by U.S. Immigration and Naturalization agents was released yesterday after spending a night in jail and posting $1,000 bond.

Dessima Williams, 33, charged at a press conference that her arrest on charges of violating immigration laws was "linked" to her sharp criticism of the U.S.-led invasion of Grenada and was timed to coincide with its first anniversary.

Williams was apprehended by INS agents shortly after she walked outside a Howard University auditorium where she had just given a speech.

Bradley G. Stevens, deputy director of the INS Washington office, said the arrest was "a routine immigration matter." He said Williams had remained in the country illegally after her diplomatic visa was invalidated in January.

"We categorically deny that this was politically motivated," Stevens said. He said the arrest took place Thursday because investigators had "just received information" that she was would be speaking at the Howard meeting, where her appearance had been publicized by its sponsors.

Williams, who had been a graduate student at American University, was appointed as Grenada's ambassador to the Organization of American States in March 1979. That was shortly after the left-wing government of Maurice Bishop came to power through a coup. She served in that capacity until after Bishop was killed by a hard-line Marxist faction on Oct. 19, 1983. U.S. troops landed on the island six days later, along with soldiers from seven Caribbean nations.

President Reagan and leaders of the Caribbean countries involved said the action was taken at the request of Grenada's governor-general and to protect American medical students on the island.

Grenada now is preparing for elections on Dec. 3.

Yesterday Williams said she had been back to Grenada briefly after the present interim government was installed last November. She said she had also visited Europe, but has spent most of past year living in Washington and New York.

She said she now lives in an apartment near Dupont Circle, and has been a full-time graduate student at American University since late August, supported by two private grants.

Her lawyer, Michael Maggio, said she had not applied for a student visa but had been making plans to seek permanent residence status as a former diplomat.

"I have been living publicly," Williams said yesterday. "I never had any intention of violating U.S. immigration laws."

Robert Neptune, Director of the INS Washington office, initally set bond for Williams at $3,500. But after a 2 1/2 hour hearing, immigration Judge Joan Arrowsmith reduced the bail to $1,000. Williams was ordered to appear a preliminary deportation hearing on Nov. 27.

At yesterday's hearing, Jacqueline Jackson, wife of the Rev. Jesse Jackson, offered to take personal custody of Williams. Other witnesses on her behalf included Josephine Butler, the Statehood Party candidate for D.C. City Council who also is a board member of the pro-Bishop U.S.-Grenada Friendship Society, and Gene Locke, administrative assistant to Rep. Mickey Leland (D-Texas).

In January 1980 the Grenada government appointed Williams as its ambassador to the United States, but the Carter administration refused to accept her credentials.

State Department sources said in September 1980 that the action was taken because Williams was allegedly implicated in a gun-running scheme out of Washington in which two Grenadians were arrested immediately before Bishop's 1979 coup. The sources said Williams was spared indictment only because her OAS appointment gave her diplomatic immunity. Williams has denied the allegations.