Washingtonian magazine publisher Phillip Merrill said yesterday that the monthly publication has crossed the 100,000 circulation mark and will continue to grow in both circulation and advertising in 1980.

Merrill, who also owns Baltimore magazine and publishes the five Capital Gazette newspapers in Maryland, made the prediction while insisting that Washingtonian won't become a national-circulation magazine as some have proposed.

In a speech to the Advertising Club of Metropolitan Washington Inc., Merrill emphasized that he has no plans to alter the magazine's content dramatically but already had made significant changes in its business operations.

Since Merrill bought the magazine last February, he has ended the Washingtonian's ventures in book publishing, conference management and selling "trinkets and guidebooks," he noted.

Further, Merrill said he increased the magazine's editorial budget by 40 percent, added two "subeditors," expanded the sales staff from six to nine, and "stripped clear excess management time and effort."

But Merrill said the magazine, which was founded in 1965, isn't interested in stressing investigative journalism. Merrill said he wants to "project a positive image of Washington" and does not want to "be a part of the same absolutely hardened go-get-em attitude" that he said characterizes the reporting of the city's newspapers.

In an interview, Merrill also said he has no current plans to add any new publications to his holdings.