D.C. mayoral candidate Patricia Roberts Harris said last night that if she is elected she will begin immediately to combat the District's 11 percent unemployment rate with a comprehensive program that could include transporting city residents to jobs in the suburbs.

Harris made the proposal during the taping of a roundtable forum for the four Democratic and two Republican candidates for mayor in the Sept. 14 primary. The 90-minute forum, sponsored by The League of Women Voters and WJLA-TV (Channel 7), will be televised on Channel 7 at 3 p.m. Saturday.

"When I am elected I will treat joblessness in this city as an emergency situation," said Harris. "We will pull every resource we have, not just in D.C., but in the Washington metropolitan area into dealing with this emergency . . . .I would begin an aggresive program to place people in the city in jobs as far away as Reston."

"There are companies around Washington now bringing people from Appalachia to fill jobs," Harris said.

City Council Member John L. Ray, (D-At Large), said he would deal with the city's high unemployment rate with tax breaks for businesses and designating city-owned land for construction of new businesses.

Ray said that Mayor Marion Barry "has focused only on downtown developemnt. All of the city cannot work downtown in law firms and lobbying associations."

Council member Charlene Drew Jarvis (D-Ward 4) joined the exchange to say the city's schools and its university are not training students for jobs available, such as those for paramedics.

Barry responded to questions on unemployment with a promise to begin a program next year in which every businessman in the city would be asked to hire one youngster for the summer. He said this would add 18,000 jobs to the city's current Summer Youth Employment Program.

Republicans E. Brooke Lee and James Edward Champagne both defended Reagan's record on jobs, with Champagne noting that most of the funds for the city's summer jobs program, as well as a recent increase in the federal payment to the District came from a Republican president.

In a separate taping at WJLA-TV last night, former City Council chairman Sterling Tucker resurrected an idea that most city leaders have given up for dead and declared that the District should pressure Congress for the right to impose a commuter tax on nonresidents who work in the city.

"I know people say you can't do it," said Tucker, at a forum for Democratic candidates in the City Council Chairman's race that also will be televised Saturday.

Incumbent Chairman Arrington Dixon and Ward 1 Council member David A. Clarke, who are competing with Tucker in the Sept. 14 primary election, did not have an opportunity to respond to Tucker's idea during the program. Both said later that they favor such a tax but that it is not likely to be approved because of intense opposition in Congress.

Clarke called the idea "wishful thinking" while Dixon said "There are more realistic issues."