Montgomery County police early yesterday arrested a 21-year-old Miami man wanted by Prince George's authorities for assault with intent to murder. The arrest came about 24 hours after the man had left an unguarded hospital ward where he was recovering after being shot during a gunfight with undercover narcotics detectives in Hyattsville.

Rickie A. Howard, 21, apparently walked out of the Washington Hospital Center Thursday after District police failed to honor a Prince George's request that a guard be stationed at the hospital. District police said that they believed Howard was so seriously wounded that a guard was not needed.

Montgomery County police spokesman Cpl. Philip Caswell said yesterday that acting on a tip phoned in to Prince George's police, about a dozen Montgomery officers, including members of the SWAT team, went to 75 East Wayne Ave., Silver Spring, about 3 a.m. Caswell said officers found Howard in an apartment, and that he was arrested without incident.

Two other men, Ansel W. Powell, 25, and Joseph G. Atkins, both of the Wayne Avenue address, were charged with harboring a fugitive, officers said. Howard was being held at Prince George's County jail without bond.