PHILADELPHIA (AP) _ Presses at The Philadelphia Inquirer started printing today's editions 51/2 hours after janitors settled a strike that kept 750,000 readers from getting Sunday papers.

Janitors and porters, who had been working almost a year without a contract, reached an agreement with Philadelphia Newspaper Inc. shortly after 5 p.m. Sunday, Teamsters Local 628 president James P. Donahue said.

The presses for Sunday editions were shut down when the janitors called a strike shortly after midnight and delivery-truck drivers, also represented by the Teamsters, honored the picket lines.

William Broom, Philadelphia Newspapers vice president of public affairs, said the Inquirer's Monday editions should hit the streets on time. Presses printing Monday papers started up approximately 1 hours late at about 10:30 p.m., editors said.

''It's been very expensive,'' Broom said of the one-day walkout, which left behind the inside sections to 750,000 copies of the bulky, ad-packed Sunday paper. The feature sections are printed in advance.

Only about 250,000 complete copies of the Sunday Inquirer, which sells for $1, were printed and distributed, Broom said. Sunday circulation is normally more than 1 million.

Donahue said the new 16-month agreement calls for a weekly wage increase of $58.50, plus added health and pension benefits.

Janitors, porters and elevator operators averaged $340 a week in wages and benefits under the old agreement, Broom said.

William Gullifer, secretary-treasurer of Local 628, said the union would vote on whether to ratify the agreement sometime this week.