The Washington area will again have a full-time Spanish-language radio station when WMDO "Radio Mundo" begins broadcasting here Monday.

Representatives of the new station say WMDO will provide news, public service announcements and contemporary music from Latin America with heavy emphasis on Caribbean music. A seven-member news staff will cover local and national news and relay it to other Spanish-language stations in the country, officials said.

The 5,000-watt station will broadcast on a flexible sunrise-to-sunset schedule ranging from 7:15 a.m. to 4:45 p.m. in the winter to 4:45 a.m. to 7:30 p.m. in the summer. The station will be heard within a 50-mile radius of its transmitter located in Wheaton.

The station replaces WDON, a defunct religious station, at 1540 on the AM dial.

WMDO is owned by the Lotus Communications Corporation, which owns a chain of all-Spanish stations across the country. It paid almost $2 million to buy and start up the new station, according to Lotus executive vice president Norman L. Posen.

The Washington area has been without an all-Spanish station since WFAN, nicknamed Radio Latina, went off the air in April 1978. A few local stations, such as WHUR-FM and WPFW-FM, include Spanish language segments in their programming but only for brief periods.

Latino leaders have been advocating an all-Spanish station like WMDO for some time. "This is the beginning of a new day, to have a radio station for all of our community," said Miguel Sandoval, president of the National Alliance for Spanish-Speaking People.

WMDO officials said they felt the Washington area presented a fertile market for an all-Spanish station, citing it as "the international headquarters for Central and South American political and economic refugees." Officials said they will rely on both local and national advertising for revenue and appeal to both "Anglo" and Hispanic advertisers.

Lotus officials commissioned a $60,000 market study that they say shows there are almost 160,000 Hispanics in the Washington metropolitan area. The 1980 U.S. census placed the Hispanic population in the area at 94,930.