Democratic gubernatorial candidate Parris N. Glendening has begun a major advertising blitz that will keep him on the air in Baltimore through the Sept. 13 primary.

A commercial that began running on area television stations Thursday night highlights Mr. Glendening's fiscal achievements as Prince George's County executive. A more general 30-second spot began airing yesterday.

The campaign expects to spend at least $1 million on the ads in the next five weeks, according to spokesman David Seldin. The commercials will run about 10 times a day on Baltimore stations, as well as on cable television in the Washington area, he said.

"Clearly Parris is less well known in Baltimore and there's a greater need to introduce him to voters there," Mr. Seldin said.

While Mr. Glendening goes to the airwaves to try to nail down a race he has led in the polls for weeks, his opponents have stepped up their attacks on him.

Lt. Gov. Melvin A. Steinberg has taken to calling his rival "Spendening" to highlight promises Mr. Glendening has made that would increase state spending by an estimated $300 million.

Yesterday, state Sen. Mary H. Boergers of Montgomery County held a press conference outside Mr. Glendening's Upper Marlboro office to criticize his record on education in Prince George's County.

A former teacher, Ms. Boergers used a chalkboard as a prop and gave Mr. Glendening an "F" in education, noting that the county's students have the second worst test scores in the state.

"Once again, the record doesn't back up his campaign rhetoric," Ms. Boergers said.

Mr. Glendening's spokesman stressed instead that the county doubled its per-pupil spending on education during his 12-year tenure. "Even during the recession when they were cutting spending on other areas of government, spending on education increased," Mr. Seldin said.

The timing of the ads had nothing to do with attacks from other candidates, Mr. Seldin said.

One of Mr. Glendening's commercials shows him confidently leading a board meeting while a narrator says he is the one candidate with "the executive experience and proven financial ability Maryland needs."

The advertisement also quotes favorable assessments of Prince George's County's finances from two New York bond-rating houses.

While the county does have a solid reputation among bond-rating houses, as recently as 1991, its rating was lowered because of an $80 million operating deficit.

Since then, however, the major houses have upgraded the county's rating to above average or excellent.

Mr. Steinberg is the only other Democrat to have aired television commercials. None of the Republican candidates has done so.