A convention center in downtown Washington would create 6,300 new jobs for the metropolitan area's economy, according to a study released yesterday by the District government.

Most of the jobs would be in the city concentrated in semi-skilled and services occupations - the very sectors where city unemployment has been growing in an era of overall economic growth for the metropolitan area.

As of last night, however, the Capitol Hill impasse that has thwarted the city's plans to build a $110 million convention center near Mt. Vernon Square remained. House and Senate conferees are divided on the issue, with Sen Patrick Leahy (D-Vt.) leading his colleagues in adamant opposition to initial spending for the complex, which is planned for a 9.7-acre site.

Several business community leaders reportedly are seeking a meeting with Leahy. They went to discuss the convention center idea and some suggestions that local businesses provide initial investments - money the businesmen claim doesn't exist in a community without big industry.

The employment study, prepared by the D.C. Department of Manpower, comes on the heels of revised unemployment figures for the city that show a deteriorating economic trend.

The number of jobless in D.C. has increased from 26,000 in 1975 to a record 32,000 last year at a time when national and metropolitan unemployemtn rates have declined. Although the total number of D.C. jobs has increased, the gains have been in white-collar categories, professionals and service industry workers.

Fewer jobs now exist in the D.C. labor market for such sectors as manufacturing, construction and retail trade - business that traditionally offered jobs for less skilled workers.

Given national trends of job gains for suburban dwellers, whites and residents of the South or West. "it is not surprising that residents of Washington - a largely black city with high rates of female labor force participation and a large youth population - continue to suffer from recession levels of unemployment," the D.C. agency stated.

Although the new report does not take a stand on the controversy over building a convention center, it calculates that if construction takes place there would be a significant improvement in the city's growing unemployment problem. Among the conclusions:

Of 6,300 new permanent jobs, about 4,000 would be located within D.C. with the balance in the suburbs - mainly at hotels and cating establishments that would attract convention-goer business. In addition, more than 2,600 jobs would be created for the construction period alone.

Most of the new permanent jobs would be in the kins of occupations most lacking in the city's economic base, thus reducing jobless rolls.

Permanent jobs created by a convention center would have what economists call a "multiplier effect" on the entire regional economy - as spending created by incomes to new workers spreads out and creates other business expansion.

To make certain that unemployed D.C. residents benefit from construction of a center, constractors could be required to hire city residents, government training funds could be allocated to prepare unemployed persons for hotel work and the city government could concentrate job placement efforts on business that would be most affect by construction of a center.

The D.C. agency said it used the most conservative assumptions in previous economic studies about the increased number of conventions an visitors that such a complex would attract. A study by Gladstone Associates for city concluded that a convention center would generate $100 million a year in new spending by delegates and exhibitors.