"The more that you know about the job market," says Ray Harris of the Prince George's Community College Career/Job Placement Center, "the better off you are."

He and other Washington counselors suggest these sources for researching another city and its job opportunities without leaving home:

* Check the library for the Encyclopedia of American Cities and Encyclodepia Americana for city profiles--also business-oriented publications, the National Geographic. Ask a reference librarian for help.

* Get a computer printout of information sources in the city of your choice from the National Referral Center of the Library of Congress. When job counselor Penny Garner surveyed Houston, the center produced a list of 60.

* Subscribe to the local newspaper for a few months to find out from the want ads who is hiring. Read the business pages for trends.

* Write to the city's Chamber of Commerce for information on the business outlook. "Nine times out of 10," says Harris, "they'll overwhelm you with material."

* Consult out-of-town phone directories (at the Martin Luther King Library or C & P office, 725 13th St. NW) for firm names.

* At the Federal Communications Commission, ask to see community ascertainment statements filed by TV stations. "They contain a lot of unusual information" about community problems and goals, says Marilyn Shook.

* Talk to state delegations on Capitol Hill, to state lobbying offices, to members of state societies. "Capitol Hill," says Garner, "is filled with people from somewhere else."

* If particular firms interest you, write for their annual reports.

* Talk to anybody you know from the city of your choice. "If Cousin Ned knew somebody in Oregon in the '60s," says Harris, "give him a call."

* Check in with trade and professional associations, many of which have headquarters in Washington, for out-of-town openings.

"Approach these people in a fairly focused and low-key way," cautions Garner, "remembering that they are not a job-hunting service."