MoveOn.org is pressuring centrist Democratic senators on health care with a new ad campaign urging them to support a government-run option as part of broad legislation lawmakers will mark up next month.

    The liberal advocacy group announced Friday that it would run radio ads targeting five Democratic senators and centrist Republican Sen. Olympia Snowe (Maine). The Democrats under pressure are Sens. Kent Conrad (N.D.), Ron Wyden (Ore.), Tom Carper (Del.), Maria Cantwell (Wash.) and Bill Nelson (Fla.).

    All six sit on the Senate Finance Committee, which has jurisdiction over a major portion of health care reform, including finding ways to pay for it. Of the group, Wyden faces reelection in 2010.

    MoveOn.org has also organized "thousands" of members, including doctors, nurses and small-business owners, to visit senators' district offices to call on them to support the so-called public plan option.

    "President Obama and 70 percent of voters support health care reform that includes a public health insurance option to contain costs, increase competition and guarantee coverage," the narrator in the ad states.

    "The insurance industry says with new rules they can do it alone, but they'll find a way to put profits first. We need a health insurance choice not run by the insurance companies to keep costs down and ensure access to quality, affordable care."

    The question over whether to make the public plan option available in all parts of the country has emerged as one of the thorniest of the health care debate. Republicans say a nationwide public plan option would be a "non-starter" and would represent a march toward a single-payer, socialized health care insurance system. They argue that government competition would drive private health care companies out of business.

    The campaign calls to mind an effort liberal advocacy groups waged earlier this year to pressure centrist Democrats to support President Obama's budget proposal.

    Health care reform has become an increasingly contentious topic between centrist Democrats and groups on the party's left wing. Last week, three major labor unions, including the American Federation of State, County and Municipal Employees, launched ads in Oregon criticizing Wyden for a proposal he drafted that has attracted the support of Republican leaders.

    Wyden's plan does not call for a government-run health care option to be made available across the country, as liberals want. He would limit the public option to underserved areas of the country where Americans can choose only between two or fewer private plans.

    The contest between liberal advocates and centrist Democrats seeking to attract broad GOP support for a reform plan will heat up next month. The Senate Health, Education, Labor and Pensions Committee is scheduled to hold its first walk-through of draft legislation June 2-3. The committee is scheduled to begin marking up the bill June 16.

    The Senate Finance Committee is expected to follow and mark up its own bill, which would pay for the massive overhaul.